# Given that f(x)=2x -5, how do you find the value of x that makes f(x)=15?

Dec 8, 2016

$x = 10$

#### Explanation:

$\setminus \textcolor{red}{f \left(x\right) = 2 x - 5}$ and $\setminus \textcolor{red}{f \left(x\right)} = 15$
therefore...
$2 x - 5 = f \left(x\right) = 15 \setminus \Rightarrow 2 x - 5 = 15$
so you now have an equation to solve:
$2 x - 5 = 15$

add 5 to both sides... $2 x \setminus \cancel{- 5 + 5} = 15 + 5$
simplify $2 x = 20$
divide both sides by 20... $\frac{\setminus \cancel{2} x}{\setminus} \cancel{2} = \frac{20}{2}$
simplify $x = \frac{20}{2} = 10$