# How do you find the slope for y=18?

Sep 19, 2016

$0$

#### Explanation:

$y = 18$ allocates a constant value of 18 to y.

So no mater what value $x$ is $y$ will always be 18

The result is a straight line that is parallel to the x-axis and the line passes through the point on the y-axis $\left(x , y\right) \to \left(0 , 18\right)$

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Mathematically:

The slope is $\left(\text{change in y")/("change in x}\right)$

Let any point ${P}_{1} \to \left({x}_{1} , {y}_{1}\right) = \left({x}_{1} , 18\right)$

Let another point ${P}_{2} \to \left({x}_{2} , {y}_{2}\right) \to \left({x}_{2} , 18\right)$ where ${P}_{1} \ne {P}_{2}$

Then slope $\to m \to \left(\text{change in y")/("change in x}\right) = \frac{{y}_{2} - {y}_{1}}{{x}_{2} - {x}_{1}} = \frac{18 - 18}{{x}_{2} - {x}_{1}} = 0$