# How do you use substitution to find x=-2 for f(x) = -x^4+8x^3+13x-4?

$f \left(- 2\right) = - 110$
$\text{substitute x = - 2 into "f(x)" and evaluate}$
$f \left(\textcolor{red}{- 2}\right) = - {\left(\textcolor{red}{- 2}\right)}^{4} + 8 {\left(\textcolor{red}{- 2}\right)}^{3} + 13 \left(\textcolor{red}{- 2}\right) - 4$
$\textcolor{w h i t e}{\times \times} = - 16 - 64 - 26 - 4 = - 110$