# How do you evaluate -a ( a ^2 + 2a - 1) for a = 2?

Apr 22, 2016

-14

#### Explanation:

In substitution, we replace something for something else, in this case anytime we see $a$, we put a 2 there. Applying this:
$- 2 \left({2}^{2} + 2 \left(2\right) - 1\right) = - 2 \left(4 + 4 - 1\right)$
$= - 2 \left(7\right)$
$= - 14$

Apr 22, 2016

$- 14$

#### Explanation:

color(blue)(-a(a^2+2a-1) $\text{for}$ $a = 2$

Now substitute the value of $a$ into the equation

$\rightarrow \underbrace{- a} \left(\underbrace{{a}^{2}} + 2 \underbrace{a} - 1\right)$

$\rightarrow - 2 \left({2}^{2} + 2 \left(2\right) - 1\right)$

$\rightarrow - 2 \left(4 + 4 - 1\right)$

$\rightarrow - 2 \left(7\right)$

color(green)(rArr-14