# If f(x) = 2x^2- x , what is f(-3)?

Aug 13, 2016

$f \left(- 3\right) = 21$

#### Explanation:

To evaluate f( -3) substitute x = - 3 into f(x)

$\Rightarrow f \left(\textcolor{red}{- 3}\right) = 2 {\left(\textcolor{red}{- 3}\right)}^{2} - \left(\textcolor{red}{- 3}\right)$

$= \left(2 \times 9\right) + 3 = 21$

Aug 13, 2016

$f \left(- 3\right) = 21$

#### Explanation:

For any function $f \left(x\right)$ to find $f \left(a\right)$ for a constant number $a$, we have just put $x = a$ in $f \left(x\right)$ and we get $f \left(a\right)$.

As $f \left(x\right) = 2 {x}^{2} - x$,

f(-3)=2×(-3)^2-(-3)

= 2×9+3

= $18 + 3 = 21$