# How do you evaluate the function f(x) = -x^2 + 3x-1 for f(-1)?

Nov 6, 2015

The most obvious way is to replace the $x$'s in the expression with $\left(- 1\right)$ and evaluate using normal arithmetic.

#### Explanation:

If $f \left(\textcolor{b l u e}{x}\right) = - {\textcolor{b l u e}{x}}^{2} + 3 \textcolor{b l u e}{x} - 1$
then
$\textcolor{w h i t e}{\text{X}} f \left(\textcolor{red}{\left(- 1\right)}\right) = - {\textcolor{red}{\left(- 1\right)}}^{2} + 3 \textcolor{red}{\left(- 1\right)} - 1$

$\textcolor{w h i t e}{\text{XXXXXXX}} = - 1 - 3 - 1$

$\textcolor{w h i t e}{\text{XXXXXXX}} = - 5$