A linear equation is an equation for a straight line.

These are all linear equations:

y = 3x + 2

y = 5x + 7

y = 4x − 3

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## Different Forms

There are many ways of writing linear equations. They usually have constants (like “3” or “c”) and must have simple variables (like “x” or “y”).

These are linear equations

y = 2x − 5

Y/2 − 3 = 2(x + 4)

2y + 3x − 4 = 0

x = 5

y =7

The variables (like “x” or “y”) in Linear Equations do NOT have:

Exponents (like the 2 in x^{2})

Square roots, cube roots, etc

These are NOT linear equations:

Y^{3} − 5 = 0

√x − y = 7

X^{5/3} = 125

## Slope-Intercept Form

The most common form is the slope-intercept equation of a straight line:

y = mx + b

Where:

m = slope or gradient

b = y intercept

y = x

From the illustration above, we got

Slope: m = 1

Intercept: b = 0

## Point-Slope Form

Another common one is the Point-Slope Form of the equation of a straight line:

y − y_{1} = m(x − x_{1})

y − 7 = 2(x − 4)

It is in the form y − y1 = m(x − x1) where:

y1 = 7

m = 2

x1 = 4

## General Form

There is General Form of the equation of a straight line:

Ax + By + C = 0

(A and B cannot both be 0)

2x − 3y + 4 = 0

It is in the form Ax + By + C = 0 where:

A = 2

B = −3

C = 4