Maryland Math 8.AT.D.9.b

Math8th GradeAlgebraic Thinking

The Standard

Match a linear equation in the form y = mx + b to its graph.

Maryland College and Career Ready Standards for Mathematics (2025) · MODEL WITH FUNCTIONS.

Teacher's field guide

What Students Need to Do: Students use the number multiplying x to tell whether a line rises or falls and how steep it is. They use the constant to find where the line crosses the y-axis, then choose the graph that fits both.
What Mastery Looks Like: Given y = -2x + 3, a student chooses a line through (0, 3) and (1, 1). They can explain why a line with the same y-intercept but a positive slope does not match.
Common Misconceptions: Students may treat the constant as the x-intercept or count the slope from the wrong starting point. They may miss a negative sign and choose a rising line instead of a falling one.
How to Assess It: Draw lines A through (0, 3) and (1, 1), B through (0, -2) and (1, 1), and C through (0, 3) and (1, 5). Ask: Which line matches y = -2x + 3, and what tells you?

Lesson moves

Hand out four equation cards and four graph cards; students pair them and mark the y-intercept and a second point on each graph.
Draw lines through (0, 3) and (1, 1), and through (0, 3) and (1, 5); ask which fits y = -2x + 3.
Give teams four graph cards, call out an equation, and have each team hold up its match and name the slope and y-intercept.
Write y = 2x + 4 for a taxi's $4 starting fare and $2 per mile, then choose its graph from three plotted lines.

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