# How do you multiply (5x - 1) ( 8x + 5)?

Mar 11, 2017

The answer is $40 {x}^{2} + 17 x - 5$

#### Explanation:

Multiplying out these brackets gives you a quadratic equation (an equation where the $x$ term has an exponent of $2$, ${x}^{2}$).

Every time you multiply out two brackets follow these simple steps.

First multiply the first term in the first bracket by the first term in the second bracket.

$5 x \cdot 8 x = 40 {x}^{2}$

Then multiply the first term in the first bracket by the second term in the second bracket.

$5 x \cdot 5 = 25 x$

Now repeat this for the second term of the first bracket.

$- 1 \cdot 8 x = - 8 x$

and

$- 1 \cdot 5 = - 5$

The order in which you do this doesn't actually matter, you just need to multiply every term in one bracket by every term in the other bracket. However, sticking to an order helps you to not get confused.

Now collect all of the terms produced.

$40 {x}^{2} + 25 x - 8 x - 5$

And simplify.

$40 {x}^{2} + 17 x - 5$

Hope this helped!

Mar 11, 2017

$40 {x}^{2} + 17 x - 5$

#### Explanation:

$\textcolor{b l u e}{\left(5 x - 1\right)} \textcolor{red}{\left(8 x + 5\right)}$

Multiply everything in the right bracket by everything in the left

$\textcolor{red}{\textcolor{b l u e}{5 x} \left(8 x + 5\right) \text{ } \textcolor{b l u e}{- 1} \left(8 x + 5\right)}$

$40 {x}^{2} + 25 x \text{ } - 8 x - 5$

But $\text{ } 25 x - 8 x = 17 x$

$40 {x}^{2} + 17 x - 5$