Answer
$x=4.24$ and $x=-4.24$
Work Step by Step
The given equation is
$\Rightarrow -21=15-2x^2$
Add $21+2x^2$ to each side.
$\Rightarrow -21+21+2x^2=15-2x^2+21+2x^2$
Simplify.
$\Rightarrow 2x^2=36$
Divide each side by $2$.
$\Rightarrow \frac{2x^2}{2}=\frac{36}{2}$
Simplify.
$\Rightarrow x^2=18$
Take the square root of each side.
$\Rightarrow x=\pm \sqrt {18}$
Use a calculator.
$\Rightarrow x=\pm 4.24$
Hence, the solutions are $x=4.24$ and $x=-4.24$.
