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Grade 8 · Expressions & Equations · 8.EE.B.6

Why Slope Is Constant Worksheets

Free, printable, and ready to teach: a practice worksheet, homework, an exit ticket, and an answer key with step-by-step solutions — plus lesson slides you can edit. No sign-up needed.

First page of the why slope is constant practice worksheet

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Key idea

One line, one slope — similar triangles. y = mx + b: m tilts, b shifts.

Sample problems

Find the slope of y = 5x − 2 using (0,−2) and (2,8).
Now find it using (1,3) and (4,18). Should it match?
State the slope and y-intercept of y = −2x + 6.
Explain, using similar triangles, why any two points on a line give the same slope.

Common mistakes to watch for

Got different answers, which means an arithmetic slip rather than a conceptual one — on one line they cannot differ.
Said “because it is the same line”, which restates the question. Or said “because I calculated both”, which is evidence rather than a reason. The similar-triangles argument is the content of this standard.
Swapped them, giving slope 5 and intercept 3. Substituting x = 0 settles which is which: y = 5.

The answer key explains each one, so you can tell what a wrong answer means.

How to use this set

Teach with the slides (about 15 minutes), or watch the video together.
Practice with the worksheet. Questions climb from fluency to application to reasoning.
Check understanding with the exit ticket, and send the homework home.
Mark with the answer key — each answer shows the steps and the most likely mistake.

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