General Form of Equation of a Line


The "General Form" of the equation of a straight line is:

Ax + By + C = 0

A or B can be zero, but not both at the same time.

The General Form isn't always the most useful form, and you may prefer to use:

Graph of y = mx + b showing slope m and y-intercept b

The Slope-Intercept Form of the equation of a straight line:

y = mx + b

or

Graph of a line passing through point (x1, y1) with slope m

The Point-Slope Form of the equation of a straight line:

y − y1 = m(x − x1)

Example: Convert 4x − 2y − 5 = 0 to Slope-Intercept Form

We are heading for:

y = mx + b

Start with:4x − 2y − 5 = 0 Move all except y right:−2y = −4x + 5 Divide all by (−2):y = 2x − 5/2

And we are done! (Note: m = 2 and b = −5/2)

Why Use It?

It has the advantage of working well with vertical lines, which the Slope-Intercept Form and Point-Slope Form don't.

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