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

##### 2 Answers

#### Answer:

#### Explanation:

It is the case that

We also have

The shortcut is to know that if you have the form

That is the condition in this question so

'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Consider:

Multiply everything inside the right hand side bracket by everything inside the left hand side bracket.

Notice that the minus follow the

So we have:

#### Answer:

#### Explanation:

Each term in the 2nd bracket must be multiplied by each term in the 1st bracket.

That is

#(color(red)(x-y))(x+y)=color(red)(x)(x+y)color(red)(-y)(x+y)# now distribute the brackets

#=x^2+cancel(xy)-cancel(xy)-y^2=x^2-y^2#