# How do you multiply (x + 5)(x - 4)?

Jul 8, 2015

${x}^{2} + x - 20$

#### Explanation:

To multiply two polynomials, you should use the FOIL (first outside inside last) method.

$\left(x + 5\right) \left(x - 4\right) = {\underbrace{x \cdot x}}_{\textcolor{b l u e}{\text{first")) + underbrace(x * (-4))_(color(blue)("outside")) + underbrace(5 * x)_(color(blue)("inside")) + underbrace(5 * (-4))_(color(blue)("last}}}$

$\left(x + 5\right) \left(x - 4\right) = {x}^{2} - 4 x + 5 x - 20$

Simplify the last equation to get the answer:

${x}^{2} + x - 20$