L9 · Linear equations of the form y = mx + b

1. 1.

   A line has slope -1 and y-intercept 6. Write its equation.

   Answer. y = -1x + 6

   y = mx + b → y = -1x + 6.

2. 2.

   A line has slope 5 and y-intercept -1. Write its equation.

   Answer. y = 5x - 1

   y = mx + b → y = 5x + -1.

3. 3.

   A line has slope -2 and y-intercept 3. Write its equation.

   Answer. y = -2x + 3

   y = mx + b → y = -2x + 3.

4. 4.

   A line has slope 1 and y-intercept 2. Write its equation.

   Answer. y = 1x + 2

   y = mx + b → y = 1x + 2.

5. 5.

   For y = 3x + 4, find y when x = 5. Then Jonah needs 3 of that amount. What is the total they need?

   Answer. 57

   y = 3(5) + 4 = 19. Then multiply by 3: 57.

6. 6.

   A line has slope -3 and y-intercept 5. Write its equation. Write a complete answer — Nora will compare with a partner.

   Answer. y = -3x + 5

   y = mx + b → y = -3x + 5.

7. 7.

   For y = -4x + 4, find y when x = 3. Then Sam needs 2 of that amount. What is the total they need?

   Answer. -16

   y = -4(3) + 4 = -8. Then multiply by 2: -16.

8. 8.

   A line has slope 2 and y-intercept -1. Write its equation. Write a complete answer — Luis will compare with a partner.

   Answer. y = 2x - 1

   y = mx + b → y = 2x + -1.

9. 9.

   For y = -2x + -3, find y when x = 2. Then Mei needs 4 of that amount. What is the total they need?

   Answer. -28

   y = -2(2) + -3 = -7. Then multiply by 4: -28.

10. 10.

    For y = 2x + 6, find y when x = 2. Then Elena needs 5 of that amount. What is the total they need?

    Answer. 50

    y = 2(2) + 6 = 10. Then multiply by 5: 50.

11. 11.

    Think

    Theo tried this problem:
    For y = 5x + 4, find y when x = 3.
    Theo wrote 38. That is not correct. What is the right answer?

    Answer. 19

    Theo’s answer 38 is off. y = 5(3) + 4 = 19.

12. 12.

    Think

    Malik tried this problem:
    A line has slope -1 and y-intercept -4. Write its equation.
    Malik wrote y = 1x - 4. That is not correct. What is the right answer?

    Answer. y = -1x - 4

    Malik’s answer y = 1x - 4 is off. y = mx + b → y = -1x + -4.

Original extra practice. Keys are computed from the items, not guessed.