# How do you simplify (a + b)(a - 2b)?

Aug 30, 2016

When you say simplify I'm going to take it as expand since factoring an expression is sometimes a way of simplifying it.
The answer will be ${a}^{2} - 2 {b}^{2} - a b$

#### Explanation:

You simply multiply out each factor.

So you start by multiplying the $a$ in $\left(a + b\right)$ to each term in $\left(a - 2 b\right)$.
You will get ${a}^{2} - 2 a b$ as the first portion of the answer.

So now you will do the same with the $b$ in $\left(a + b\right)$.
Then you get $- 2 {b}^{2} + a b$.

Now you add ${a}^{2} - 2 a b$ and $- 2 {b}^{2} + a b$ to get ${a}^{2} - 2 {b}^{2} - a b$ .