# How do you find the equation of the line through (9,-12) with slope -1/2?

Mar 16, 2018

$y = - \frac{1}{2} x - \frac{15}{2}$

#### Explanation:

$\text{the equation of a line in "color(blue)"slope-intercept form}$ is.

•color(white)(x)y=mx+b

$\text{where m is the slope and b the y-intercept}$

$\text{here } m = - \frac{1}{2}$

$\Rightarrow y = - \frac{1}{2} x + b \leftarrow \textcolor{b l u e}{\text{is the partial equation}}$

$\text{to find b substitute "(9,-12)" into the partial equation}$

$- 12 = - \frac{9}{2} + b \Rightarrow b = - \frac{24}{2} + \frac{9}{2} = - \frac{15}{2}$

$\Rightarrow y = - \frac{1}{2} x - \frac{15}{2} \leftarrow \textcolor{red}{\text{in slope-intercept form}}$