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**Slope Intercept Form**

If a line has slope m and y-intercept b, then the equation of the line in slope-intercept form is

y = mx + b.

when b = 0, we say that y is proportional to x.

**Point-Slope from**

If a line has slope m and passes through the point (x_{1} , y_{1}), then an equation of the line is given by

y – y_{1} = m(x – x_{1}) ,

the point-slope from of the equation of a line.

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**The slope of a horizontal line is 0.**

**The slope of a vertical line is undefined.**