Grade 8 · Math

8th grade Write y = mx + b from a slope and a point, a y-intercept and a point, or two points worksheet

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Write y = mx + b from a slope and a point, a y-intercept and a point, or two points

Grade 8 Math Worksheet - Challenge Me

NameDate

Circle the best answer, or write your answer on the line.

Kira's line passes through (-3, 4) and (3, 0). What rule, written as y = mx + b, gives the line?
Luz's line passes through (-4, -1) and (4, 5). What rule, written as y = mx + b, gives the line?
Milo's line passes through (2, 5.5) and (6, 7.5). What rule, written as y = mx + b, gives the line?
Noah's line passes through (5, 3.5) and (10, 8). What rule, written as y = mx + b, gives the line?
Pia's plant is 14 cm tall at week 3 and grows 2 cm each week. Let x be weeks and y the height in cm. What rule gives y, as y = mx + b?
Zee's line passes through (1, 4) and (3, 10). What is y on the line when x = 6?
Ari's line passes through (2, 7) and (4, 3). What is y on the line when x = 5?
Bo's line passes through (-1, 1) and (2, 7). What is y on the line when x = 5?
9.
Esme wants a rule for the line through (2, 7) and (5, 16). Which rule fits both points?
- y = 3x + 1
- y = 3x
- y = x + 3
- y = 3x + 7
10.
Jun wants a rule for the line through (1, 9) and (4, 3). Which rule fits both points?
- y = -2x + 9
- y = 11x − 2
- y = -2x + 11
- y = 2x + 11

8th grade Write y = mx + b from a slope and a point, a y-intercept and a point, or two points worksheet – printable — Print: 1 2 3 4 5 6

About this worksheet

Write y = mx + b from a slope and a point, a y-intercept and a point, or two points. Every version has 10 questions, and the answer key prints on the second page.

What your child will learn

I can find the y-intercept of a line from its slope and one point, by stepping back to x = 0.
I can find the slope from a y-intercept and a point, and from two points.
I can write y = mx + b from any of these, and find y for another x.

Standard: 8.F.B.4 (a function from a description or two (x, y) values), 8.EE.B.6 (partial)

Words to know

rule: y = mx + b: every row of the table obeys it.

slope m: Output change ÷ input change: the change in y for 1 more x.

y-intercept b: The output at x = 0: the start.

step back: Use the slope to work out the row for x = 0.

point: A pair (x, y): one row of the table.

Common mistakes

Your child used the y of the point as the start.

Your child added the steps instead of taking them off.

Your child took off the slope only once.

What to say

Ask: is that point at x = 0, or further along the line?

Ask: going back to x = 0, does y get bigger or smaller for a rising line?

Ask: how many steps is it from the point back to x = 0?

Questions parents ask

What is the most common mistake with write y = mx + b from a slope and a point, a y-intercept and a point, or two points?

Your child used the y of the point as the start.

How can I help my child with write y = mx + b from a slope and a point, a y-intercept and a point, or two points?

Ask: is that point at x = 0, or further along the line?

Are these 8th grade math worksheets free to print?

Yes. All 6 printable versions at each level are free to print, with the answer key, and no account is needed.

More grade 8 math

See all grade 8 math

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