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Virginia SOL Mathematics Textbook

Algebra 1 Workbook — Chapter 8: Systems of Two Linear Equations

SOL A.EI.2 (a, b, c, h) · Companion to Textbook Chapter 8

Each page below is one Canva page. Headings are sized for direct paste: page title as H1, section labels as H2. Figures referenced by filename live in ../figures/. Every numbered item is the same problem as in the textbook, so one answer key serves both. Item numbers run continuously from 1 to 132.


PAGE 1 — Chapter opener

Chapter 8 · Systems of Two Linear Equations

Standard A.EI.2 (a, b, c, h)

In this chapter you will:

Words to know: system of two linear equations · solution of a system · ordered pair · verify · point of intersection · substitution · back-substitute · elimination · addition property of equality · equivalent equation · one solution · no solution · infinitely many solutions · parallel lines · identical lines · break-even point · viewing window · interpret

Convention: a solution of a system is an ordered pair, never a single number. "x=3x = 3" is half an answer. Check every candidate in both original equations.


PAGE 2 — What a system is

8.1 A System and Its Solution

FIGURE: fig1-a-system-and-its-solution.png (full width)

Fill in the blanks.

A solution of a system is an ordered pair that makes ____________ equations true.

On a graph, the solution is the point where the two lines ____________________.

  1. Solution of xy=1x - y = -1 and 2x+y=72x + y = 7: ____________

    What names it on the graph? _______________________________________

  2. Verify it.

Equation Substitute True?
xy=1x - y = -1
2x+y=72x + y = 7
  1. Is (0,1)(0,1) a solution? ______ Show both substitutions:



PAGE 3 — One equation is not enough

Checking Against Both Lines

FIGURE: fig7-checking-a-candidate-point.png (full width)

  1. Which of (2,3)(2,3) and (4,1)(4,1) solves x+y=5x + y = 5 and 2xy=12x - y = 1?
Point x+y=5x + y = 5 2xy=12x - y = 1 Solution?
(2,3)(2,3)
(4,1)(4,1)
  1. Explain. Why must an ordered pair satisfy both equations?



PAGE 4 — Building a system from a story

Creating a System

Three steps. ① Define each variable in a ____________ sentence, with ____________. ② Find the two independent ____________. ③ Write one ____________ per fact.

  1. Adult tickets $12, child tickets $8; 4040 tickets sold for $408.

    Let aa = _______________________________________

    Let cc = _______________________________________

    Tickets: _______________________ Dollars: _______________________

  2. Apply it. 1212 coins, nickels and dimes, worth 9595 cents.

    Let nn = ____________________ Let dd = ____________________

    Coins: ____________________ Cents: ____________________

  3. Apply it. Rectangle, perimeter 3434 cm, length 55 cm more than width.

    Let LL = ____________________ Let WW = ____________________

    Perimeter: ____________________ Relationship: ____________________

  4. Apply it. A class of 2727 has 33 more than twice as many boys as girls.

    System: ____________________ and ____________________


PAGE 5 — Practice · testing pairs

Practice · Is It a Solution?

  1. System: 3x+y=113x + y = 11 and x2y=6x - 2y = 6.
Pair First equation Second equation Solution?
a) (4,1)(4,-1)
b) (2,5)(2,5)
c) (0,11)(0,11)
d) (2,4)(-2,-4)
  1. Verify (3,2)(-3,2) in 2x+5y=42x + 5y = 4 and xy=5x - y = -5: _______________________________________

  2. Apply it. Ride Rite: $3 plus $2 per mile. Cab Co: $7 plus $1 per mile.

    Let xx = ____________________ Let yy = ____________________

    System: ____________________ and ____________________

  3. Explain. Why can a system of two linear equations never have exactly two solutions?


  4. Find the error. A student says (1,4)(1,4) solves x+y=5x + y = 5 and 2xy=42x - y = 4 "because 1+4=51 + 4 = 5."

    What went wrong? _______________________ Correct solution: ____________

  5. Technology. Steps to check (4,1)(4,-1) in 3x+y=113x + y = 11, x2y=6x - 2y = 6 on a calculator:


  6. Apply it. 33 notebooks and 22 pens cost $13; 55 notebooks and 44 pens cost $23.

    Let nn = ____________________ Let pp = ____________________

    System: ____________________ and ____________________


PAGE 6 — Exit ticket 8.1

Exit Ticket · Lesson 8.1

Name: ________________________ Date: ____________

  1. Is (5,2)(5,-2) a solution of x+y=3x + y = 3, 2x+3y=42x + 3y = 4? ______ Show both: ____________

  2. Is (1,6)(1,6) a solution of y=4x+2y = 4x + 2, 3x+y=103x + y = 10? ______ Show both: ____________

  3. 99 fish, twice as many tetras as guppies. System: ____________ and ____________

  4. Explain. What is a solution of a system, and why is it an ordered pair?



PAGE 7 — Solving by graphing

8.2 Solving a System by Graphing

FIGURE: fig6-graphing-a-system.png (full width)

Four steps. ① Solve each equation for ______. ② Graph ______ lines. ③ Read the ____________ point. ④ ____________ in both original equations.

  1. 2x+y=82x + y = 8 \rightarrow ____________________ xy=1x - y = 1 \rightarrow ____________________

    Solution: ____________

  2. Verify in the originals: _______________________________________

  3. From the one-solution figure: solution of y=2x3y = 2x - 3, y=x+3y = -x + 3: ____________

    Verify: _______________________________________


PAGE 8 — Graphing practice

Practice · Read the Crossing

FIGURE: fig11-blank-grids-systems.png (full page, use Grids A–D)

  1. y=x+2y = x + 2 and y=2x+5y = -2x + 5 Solution: ____________ Verified? ______

  2. y=12x1y = \tfrac12 x - 1 and y=x+5y = -x + 5 Solution: ____________ Verified? ______

  3. Solve each by graphing.

System Solution Check in both?
a) y=x4y = x - 4, y=2x+5y = -2x + 5
b) y=3x+2y = -3x + 2, y=x6y = x - 6
c) x+y=1x + y = 1, y=2x+4y = 2x + 4
d) y=12x+1y = \tfrac12 x + 1, y=12x+3y = -\tfrac12 x + 3
  1. Rewrite, then graph.
System Slope-intercept forms Solution
a) 3x+y=53x + y = 5, xy=3x - y = 3
b) x+2y=8x + 2y = 8, y=x2y = x - 2
c) 2xy=42x - y = 4, x+y=5x + y = 5
  1. y=2x+1y = 2x + 1 and y=2x3y = 2x - 3 Number of solutions: ____________ Why? ____________

  2. y=x+3y = -x + 3 and 2x+2y=62x + 2y = 6 Number of solutions: ____________ Why? ____________


PAGE 9 — The window that lies

When the Picture Is Incomplete

FIGURE: fig9-window-that-lies.png (full width — do not place text beside it)

  1. Explain. What does the left panel appear to show? Why is that reading wrong?


    What did the slopes tell you first? _______________________________________

  2. Technology. Graph y=1.5x+2y = 1.5x + 2 and y=1.6x2y = 1.6x - 2.

    Window used: ____________________ Intersection: ____________

    Algebraic confirmation: _______________________________________

  3. Explain. When does graphing give an exact answer, and what should you do when it does not?


  4. Find the error. A student graphs y=3x1y = 3x - 1 and y=3x+4y = 3x + 4 and reports "about (6,17)(6,17)."

    What went wrong? _______________________ Correct answer: ____________


PAGE 10 — Systems in a context graph

Reading a Break-Even Point

FIGURE: fig8-context-two-ride-plans.png (half width)

  1. Apply it. Solution: ____________

    In a sentence, with units: _______________________________________

    Cheaper for 22 miles: ____________ Cheaper for 1010 miles: ____________

  2. Apply it. Dana: $60 saved, $5 a week. Eli: $100 saved, $3 a week.

    System: ____________________ and ____________________

    Window needed: ____________________ Solution: ____________

  3. Apply it. Cost y=4x+120y = 4x + 120; revenue y=10xy = 10x.

    Solution: ____________ What it means: _______________________________________

  4. Graph x=2x = -2 and y=4y = 4. Solution: ____________

    Why can x=2x = -2 not be written as y=mx+by = mx + b? _______________________________________


PAGE 11 — Exit ticket 8.2

Exit Ticket · Lesson 8.2

Name: ________________________ Date: ____________

  1. y=x1y = x - 1, y=x+5y = -x + 5 Solution: ____________ Verified? ______

  2. x+y=4x + y = 4, y=2x+1y = 2x + 1 Solution: ____________ Verified? ______

  3. Two lines both fall 44 units per 11 unit right and cross the yy-axis at different points.

    Number of solutions: ____________ Why? _______________________________________

  4. Technology. No crossing on the standard window, but the slopes differ. Conclusion and next step:



PAGE 12 — Substitution

8.3 Solving by Substitution

Five steps. ① ____________ one variable in one equation. ② Substitute into the ____________ equation. ③ Solve the ____________-variable equation. ④ ____________-substitute. ⑤ Write the ____________ pair and verify.

  1. y=3x2y = 3x - 2, 2x+y=82x + y = 8

    Substituted equation: _______________________ x=x = ______ y=y = ______ Pair: ____________

  2. x=y+3x = y + 3, 2x+5y=132x + 5y = 13 Pair: ____________

  3. y=2x+9y = -2x + 9, y=4x3y = 4x - 3 Set equal: _______________________ Pair: ____________

  4. x+y=7x + y = 7, 3x2y=63x - 2y = 6 Isolated: ____________________ Pair: ____________

  5. Verify item 45.

Equation Substitute True?
x+y=7x + y = 7
3x2y=63x - 2y = 6
  1. Explain. Why is substitution easiest when a variable has coefficient 11 or 1-1?



PAGE 13 — Substitution practice

Practice · Substitute and Solve

  1. A variable is already isolated.
System Substituted equation Solution
a) y=2x+1y = 2x + 1, 3x+y=113x + y = 11
b) x=3y1x = 3y - 1, 2x+y=122x + y = 12
c) y=x+6y = -x + 6, 4xy=94x - y = 9
d) y=5xy = 5x, x+y=18x + y = 18
  1. Isolate first. Say which variable you chose and why.
System Variable isolated Solution
a) x+2y=11x + 2y = 11, 3xy=53x - y = 5
b) 2x+y=12x + y = -1, 5x3y=255x - 3y = 25
c) x4y=2x - 4y = -2, 3x+2y=83x + 2y = 8
  1. y=3x+1y = 3x + 1, 6x2y=56x - 2y = 5 Statement you end with: ____________

    Solutions: ____________________ Picture: ____________________

  2. y=4x+5y = -4x + 5, 8x+2y=108x + 2y = 10 Statement you end with: ____________

    Solutions: ____________________ Picture: ____________________


PAGE 14 — Substitution in context

Apply It · Substitution

  1. Apply it. Two numbers: sum 4646, difference 1212.

    System: ____________________ and ____________________ Numbers: ______ and ______

  2. Apply it. Solve your item 11 rectangle. Width: ______ cm Length: ______ cm

  3. Apply it. Solve your item 12 class. Boys: ______ Girls: ______

  4. Apply it. Plan A: $25 plus $0.10 per minute. Plan B: $15 plus $0.15 per minute.

    System: ____________________ and ____________________ Solution: ____________

    In a sentence, with units: _______________________________________

  5. Explain. Name a system where substitution is clearly better, and one where it is painful.


  6. Find the error. A student substitutes y=2x1y = 2x - 1 back into that same equation and gets 2x1=2x12x - 1 = 2x - 1.

    What went wrong? _______________________________________________

    Correct work with 4x2y=24x - 2y = 2: _______________________ Solutions: ____________

  7. y=x+4y = x + 4, 3x+2y=233x + 2y = 23 Solution: ____________ Graphical confirmation: ____________


PAGE 15 — Exit ticket 8.3

Exit Ticket · Lesson 8.3

Name: ________________________ Date: ____________

  1. y=4x7y = 4x - 7, 2x+y=112x + y = 11 Solution: ____________

  2. x=2y+1x = 2y + 1, 3xy=83x - y = 8 Solution: ____________

  3. x+y=9x + y = 9, 2xy=32x - y = 3 Isolated: ____________ Solution: ____________

  4. Apply it. Solve your item 19 fish tank. Guppies: ______ Tetras: ______


PAGE 16 — Elimination

8.4 Solving by Elimination

Five steps. ① Line up ____________ terms. ② Make one pair of coefficients ____________. ③ ____________ the equations. ④ Solve for the surviving variable. ⑤ Back-substitute, write the pair, and ____________.

  1. x+y=10x + y = 10, xy=4x - y = 4 Sum: ____________ Solution: ____________

  2. 3x+2y=163x + 2y = 16, x2y=0x - 2y = 0 Sum: ____________ Solution: ____________

  3. 2x+3y=122x + 3y = 12, xy=1x - y = 1 Multiplied ______ by ______ Solution: ____________

  4. 3x+4y=103x + 4y = 10, 2x+3y=72x + 3y = 7 Multipliers: ______ and ______ Solution: ____________

  5. Verify item 66.

Equation Substitute True?
3x+4y=103x + 4y = 10
2x+3y=72x + 3y = 7
  1. Explain. Why does adding the two equations give a true equation? Name the property.



PAGE 17 — Elimination practice

Practice · Eliminate a Variable

  1. Add or subtract as they stand.
System Variable eliminated Solution
a) x+y=12x + y = 12, xy=2x - y = 2
b) 2x+y=92x + y = 9, 3xy=113x - y = 11
c) 5x+2y=115x + 2y = 11, 3x2y=133x - 2y = 13
d) 7x+4y=27x + 4y = 2, 3x4y=183x - 4y = 18
  1. Multiply one equation first.
System Multiplier Solution
a) x+3y=7x + 3y = 7, 2xy=72x - y = 7
b) 4x+y=104x + y = 10, 3x2y=133x - 2y = 13
c) 5x2y=45x - 2y = 4, 3x+y=93x + y = 9
  1. Multiply both equations.
System Multipliers Solution
a) 2x+3y=132x + 3y = 13, 3x+2y=123x + 2y = 12
b) 4x+5y=74x + 5y = 7, 3x2y=123x - 2y = -12
  1. 2x+y=52x + y = 5, 4x+2y=34x + 2y = 3 Ends with: ____________ Solutions: ____________ Graph: ____________

  2. 3xy=63x - y = 6, 6x2y=126x - 2y = 12 Ends with: ____________ Solutions: ____________ Graph: ____________


PAGE 18 — Elimination in context

Apply It · Elimination

FIGURE: fig10-context-tickets-system.png (half width)

  1. Apply it. Solve your item 16 notebooks and pens. Notebook: $______ Pen: $______

  2. Apply it. Solve your item 5 theater. Adult: ______ Child: ______

  3. Apply it. Solve your item 9 coins. Nickels: ______ Dimes: ______

  4. Apply it. 1212 tickets, $50 taken in, adult $5 and student $3.

    System: ____________________ and ____________________ Solution: ____________

    Does it match the marked point on the figure? ______

  5. Explain. Why does multiplying one equation by a nonzero number leave the solution set unchanged? What goes wrong at 00?


  6. Find the error. Subtracting 3x+2y=53x + 2y = 5 from 5x+2y=115x + 2y = 11, a student writes 2x=162x = 16.

    What went wrong? _______________________ Solution: ____________


PAGE 19 — Exit ticket 8.4

Exit Ticket · Lesson 8.4

Name: ________________________ Date: ____________

  1. x+y=8x + y = 8, xy=2x - y = 2 Solution: ____________

  2. 2x+3y=72x + 3y = 7, 4x3y=54x - 3y = 5 Solution: ____________

  3. 3x+2y=43x + 2y = 4, xy=3x - y = 3 Multiplier: ______ Solution: ____________

  4. Apply it. Five hot dogs and two drinks cost $17; three hot dogs and four drinks cost $20.

    System: ____________________ and ____________________

    Hot dog: $______ Drink: $______


PAGE 20 — The three cases

8.5 One, None, or Infinitely Many

FIGURE: fig5-three-cases-side-by-side.png (full width — do not place text beside it)

Complete the table.

Case Slopes yy-intercepts Algebra ends with Solutions
Intersecting
Parallel
Identical
  1. Name the three cases shown, left to right: ____________, ____________, ____________

PAGE 21 — Each case up close

One, None, Infinitely Many

FIGURE: fig2-system-one-solution-intersecting.png (one-third width)

  1. Classify, and justify with the slopes: _______________________________________

FIGURE: fig3-system-no-solution-parallel.png (one-third width)

  1. Classify, and justify with slopes and intercepts: _______________________________________

FIGURE: fig4-infinitely-many-same-line.png (one-third width)

  1. Classify, and show that one equation is a multiple of the other:


  2. y=3x+1y = 3x + 1, y=3x4y = 3x - 4 Classification: ____________________ How you decided: ____________

  3. 2x4y=62x - 4y = 6, x2y=3x - 2y = 3 Classification: ____________________ How you decided: ____________


PAGE 22 — Classification practice

Practice · Count the Solutions

  1. Compare slopes and intercepts.
System Slopes Intercepts Solutions
a) y=2x+7y = -2x + 7, y=5x1y = 5x - 1
b) y=14x3y = \tfrac14 x - 3, y=14x+2y = \tfrac14 x + 2
c) y=x+8y = -x + 8, 3x+3y=243x + 3y = 24
d) 4x+y=94x + y = 9, y=4x+1y = -4x + 1
e) x+y=6x + y = 6, xy=6x - y = 6
  1. Rewrite in slope-intercept form, then classify.
System Rewritten Solutions
a) 2x+3y=62x + 3y = 6, 4x+6y=124x + 6y = 12
b) 2x+3y=62x + 3y = 6, 4x+6y=184x + 6y = 18
c) 2x+3y=62x + 3y = 6, 4x6y=124x - 6y = 12
  1. y=kx+3y = kx + 3, y=5x2y = 5x - 2 has no solution when k=k = ______

    Why can no kk give infinitely many? _______________________________________

  2. y=2x+cy = 2x + c, 4x2y=64x - 2y = -6 has infinitely many when c=c = ______

    Every other cc gives ____________________ because _______________________


PAGE 23 — Classification in context and errors

Apply It · What the Count Means

  1. Apply it. Shop A: $45 plus $3 per shirt. Shop B: $60 plus $3 per shirt.

    System: ____________________ and ____________________ Classification: ____________

    What it means for a customer: _______________________________________

  2. Explain. Why can a system of two linear equations never have exactly three solutions?


  3. Find the error. A student reaches 0=00 = 0 and writes "no solution."

    What went wrong? _______________________ Correct conclusion: ____________________

  4. Explain. Connect "the variables vanished and left a false statement" to "the lines are parallel."



PAGE 24 — Exit ticket 8.5

Exit Ticket · Lesson 8.5

Name: ________________________ Date: ____________

  1. y=3x+2y = -3x + 2, y=3x+2y = -3x + 2 Solutions: ____________ Graph: ____________________

  2. xy=4x - y = 4, 2x2y=92x - 2y = 9 Solutions: ____________ Graph: ____________________

  3. 5x+y=35x + y = 3, xy=3x - y = 3 Solutions: ____________ If one, find it: ____________

  4. Explain. The difference between ending with 0=00 = 0 and ending with 0=70 = 7:



PAGE 25 — The five-step model

8.6 Modeling with Systems

FIGURE: fig10-context-tickets-system.png (half width)

Five steps. ① Define both variables in full ____________, with ____________. ② One equation per independent ____________. ③ ____________, and say why you chose that method. ④ Verify ____________ ways. ⑤ ____________ the pair as a sentence.

  1. Apply it. Adult tickets $5, student tickets $3; 1212 tickets, $50.

    Let xx = _______________________ Let yy = _______________________

    System: ____________________ and ____________________ Solution: ____________

    Sentence: _______________________________________

  2. Apply it. Use the ride-plan figure. Variables, system, solution, and what each side of the crossing means:



PAGE 26 — Verifying three ways

Three Kinds of Evidence

  1. 3030 marbles, 66 more blue than red. System: ____________ and ____________ Solution: ____________

  2. Verify item 104 three ways.

Check What you do What you find
Algebraically
Graphically
With technology
  1. Explain your method. Name the method, the reason, the key step, and the check.


  2. 55 vehicles — vans hold 66, buses hold 2020 — carry 7878 people.

    System: ____________________ and ____________________ Solution: ____________

    Why it cannot describe the trip: _______________________________________


PAGE 27 — Modeling practice

Apply It · Build, Solve, Interpret

  1. Apply it. Gym A: $50 to join, $20 a month. Gym B: $20 to join, $25 a month.

    System: ____________ and ____________ Solution: ____________ Sentence: ____________

  2. Apply it. Garden perimeter 9696 ft, length three times the width.

    System: ____________ and ____________ Length: ______ ft Width: ______ ft

  3. Apply it. 2020 bills, twos and fives, worth $70.

    System: ____________ and ____________ Twos: ______ Fives: ______

  4. Apply it. A 2020-cm candle burns 22 cm per hour; a 1414-cm candle burns 0.50.5 cm per hour.

    System: ____________ and ____________ Solution: ____________

    Sentence: _______________________________________

  5. Technology. Check item 111. Window: ____________ Reported point: ____________ Agrees? ______


PAGE 28 — Reasoning and errors

Explain and Correct

  1. Explain. Why does substituting into only one equation prove nothing?


  2. Find the error. A student finds x=9x = 9 and writes "the solution is 99."

    What is missing? _______________________________________________

    A complete answer looks like: _______________________________________

  3. Apply it. Shop A: $45 plus $3 per shirt. Shop B: $60 plus $3 per shirt.

    Solution: ____________________ What it means for a customer: ____________________

  4. Apply it. "22 lb trail mix and 11 lb nuts for $14" and "44 lb trail mix and 22 lb nuts for $28."

    System: ____________ and ____________ Classification: ____________________

    Why the second ad adds nothing: _______________________________________


PAGE 29 — Exit ticket 8.6

Exit Ticket · Lesson 8.6

Name: ________________________ Date: ____________

  1. Apply it. 1515 questions worth 22 or 55 points each, 5151 points total.

    Let xx = _______________________ Let yy = _______________________

    System: ____________ and ____________ Solution: ____________

  2. Verify algebraically in both, and describe the graphical check:


  3. Interpret in one sentence with units: _______________________________________

  4. Technology. How you would confirm it, and what a different reported point would mean:



PAGE 30 — Chapter 8 review · creating and solving

Chapter 8 Review

Part A · Creating a system from a context

  1. Apply it. Pencils $0.50, erasers $0.75; 4040 items sold for $25.

    Let pp = ____________________ Let ee = ____________________

    System: ____________ and ____________ Solution: ____________

  2. Apply it. Sum 3232; the larger is 77 less than twice the smaller.

    System: ____________ and ____________ Numbers: ______ and ______

Part B · Solving algebraically and graphically

  1. y=x+1y = -x + 1, y=2x5y = 2x - 5 by graphing Solution: ____________ Verified? ______

  2. y=3x4y = 3x - 4, x+2y=13x + 2y = 13 by substitution Solution: ____________

  3. 3x+2y=113x + 2y = 11, 2x2y=142x - 2y = 14 by elimination Solution: ____________

  4. 4x3y=14x - 3y = -1, 2x+y=72x + y = 7 by any method Method: ____________ Why: ____________ Solution: ____________


PAGE 31 — Chapter 8 review · counting, verifying, interpreting

Chapter 8 Review (continued)

Part C · Counting the solutions

FIGURE: fig5-three-cases-side-by-side.png (full width)

  1. y=12x+4y = \tfrac12 x + 4, x2y=10x - 2y = 10 Solutions: ____________ Graph: ____________________

  2. 6x+2y=86x + 2y = 8, y=3x+4y = -3x + 4 Solutions: ____________ Graph: ____________________

  3. x+y=5x + y = 5, xy=1x - y = 1 Solutions: ____________ If one, find it: ____________

Part D · Verifying, explaining, interpreting

  1. Verify your item 126 answer three ways.
Check What you do What you find
Algebraically
Graphically
With technology
  1. Apply it. Tank A: 500500 L draining 2020 L per minute. Tank B: 200200 L filling 1010 L per minute.

    System: ____________ and ____________ Solution: ____________

    Sentence: _______________________________________

  2. Explain. Method, reason, key step, three-way verification, and whether the answer is reasonable:



PAGE 32 — Blank grids

Graph Paper

FIGURE: fig11-blank-grids-systems.png (full page)

Use these grids for any system a teacher assigns alongside this chapter: graphing two lines to find where they cross, checking an algebraic answer against a picture, or drawing the parallel pair that shows why a system has no solution.

Three reminders for every sketch:


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