# How do you multiply (5 - 8y)^2?

May 20, 2018

Multiplying ${\left(5 - 8 y\right)}^{2}$ gives $64 {y}^{2} - 80 y + 25$

#### Explanation:

Ok, so we start by rewriting it as two separate binomials.

$\left(5 - 8 y\right) \left(5 - 8 y\right)$

So now we multiplying the two binomials by the FOIL method. we have and get

$25 - 40 y - 40 y + 64 {y}^{2}$

So we would double check our work to ensure we didn't miss multiplying a number by another number, otherwise it wouldn't come out right. So we can combine like terms and get:

$25 - 80 y + 64 {y}^{2}$

But, you would want to put it to the highest degree first as some people would want that.

$64 {y}^{2} - 80 y + 25$

May 20, 2018

${\left(5 - 8 y\right)}^{2} = \left(5 - 8 y\right) \left(5 - 8 y\right) = 64 {y}^{2} - 80 y + 25$

#### Explanation:

To expand double brackets you need to multiply all of the terms in each bracket by the terms in the other bracket.

Applying the distributing rule ${\left(a - b\right)}^{2} = {a}^{2} - 2 a b + {b}^{2}$)
So expanding this one you must do:

$- 8 y \cdot - 8 y = 64 {y}^{2}$
$\left(- 8 y \cdot 5\right) \cdot 2 = - 80 y$
and $5 \cdot 5 = 25$

$64 {y}^{2} - 80 y + 25$