How do you solve 16- 4x ^ { 2} = - 20?

Jun 7, 2017

$x = \pm 3$

Explanation:

$\text{subtract 16 from both sides}$

$\cancel{16} \cancel{- 16} - 4 {x}^{2} = - 20 - 16$

$\Rightarrow - 4 {x}^{2} = - 36 \leftarrow \text{ multiply through by - 1}$

$\Rightarrow 4 {x}^{2} = 36$

$\text{divide both sides by 4}$

$\frac{\cancel{4} \textcolor{w h i t e}{x} {x}^{2}}{\cancel{4}} = \frac{36}{4}$

$\Rightarrow {x}^{2} = 9$

$\textcolor{b l u e}{\text{take the square root of both sides}}$

$\sqrt{{x}^{2}} = \pm \sqrt{9} \leftarrow \textcolor{red}{\text{ note plus or minus}}$

$\Rightarrow x = \pm 3$