Mrs.D Math · 8th Grade

LINE
LOCK

Slope & Y-Intercept
📈 Slope
📍 y-intercept
🔑 y = mx + b
📐 rise / run
🎯 b crosses the y-axis
🔒 y = 2x + 3
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📚 Slope & Y-Intercept

The Equation of a Line

y = mx + b

m is the slope (rise ÷ run). b is the y-intercept — where the line crosses the y-axis.

1
From a graph: find where the line crosses the y-axis. That number is b.
Crosses at (0, 3) → b = 3
2
Count the slope triangle: slope = rise ÷ run. Going down means the rise is negative!
up 2, right 1 → m = 2
3
Lock it in: put m and b into y = mx + b.
m = 2, b = 3 → y = 2x + 3

From a Table

✓
Slope first: m = change in y ÷ change in x between any two rows.
x: 1→2, y: 7→9  ⇒  m = 2 ÷ 1 = 2
✓
Then b: if x = 0 is in the table, b is that y-value. If not, work backwards or plug a point into y = mx + b and solve for b.
y = 2x + b with (1, 7) → 7 = 2 + b → b = 5

How to Play

📈
From a Graph — Read the slope triangle and y-intercept dot, then pick the matching equation.
📊
From a Table — Find the pattern in the table, then pick the matching equation.
🆕
Mixed — Graphs and tables together for the ultimate challenge!
🧮
Calculator — Tap the gold calculator button any time. But try it in your head first!
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