# How do you find the sum or difference of #(8y-4y^2)+(3y-9y^2)#?

##### 1 Answer

#### Explanation:

When adding or subtracting you can not mix 'types' (variables)

Suppose that instead of adding the two brackets we had a subtraction.

Think of:

Multiply everything inside the bracket by +1 giving:

..........................................................................

Think of:

Multiply everything inside

.......................................................................

Sometimes it is helpful to think of add as 'put with' and subtract as 'remove from'