Example

Finding the Equation of a Horizontal Line Through (1,2)(-1, 2) Using Point-Slope Form

To find the equation of a horizontal line that passes through the point (1,2)(-1, 2), use the point-slope form with a slope of zero.

Step 1 — Identify the slope: Every horizontal line has slope m=0m = 0.

Step 2 — Identify the point: (x1,y1)=(1,2)(x_1, y_1) = (-1, 2).

Step 3 — Substitute into the point-slope form yy1=m(xx1)y - y_1 = m(x - x_1):

y2=0(x(1))y - 2 = 0(x - (-1))

y2=0(x+1)y - 2 = 0(x + 1)

Step 4 — Simplify: Since any number multiplied by zero is zero, the entire right side vanishes:

y2=0y - 2 = 0

y=2y = 2

The equation is y=2y = 2, which is already in the form y=ay = a characteristic of horizontal lines. It could also be written as y=0x+2y = 0x + 2 to show the slope-intercept form explicitly. This example confirms that applying the point-slope procedure with m=0m = 0 always produces a horizontal line equation y=y1y = y_1, where y1y_1 is the y-coordinate of the given point.

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Updated 2026-04-21

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