Example

Finding the Equation of a Line with Slope 9-9 and yy-Intercept (0,4)(0, -4)

To find the equation of a line when the slope and yy-intercept are given, substitute these values into the slope-intercept form, y=mx+by=mx+b.

Step 1 — Identify the given values. The slope is m=9m = -9 and the yy-intercept is (0,4)(0, -4), meaning b=4b = -4.

Step 2 — Substitute into the slope-intercept form. Replace mm with 9-9 and bb with 4-4 in the equation y=mx+by=mx+b:

y=9x+(4)y = -9x + (-4)

Step 3 — Simplify. Rewrite the addition of a negative as subtraction:

y=9x4y = -9x - 4

The equation of the line is y=9x4y = -9x - 4. This procedure works because the slope-intercept form is a direct template for these two specific qualities of a line.

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Updated 2026-05-03

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