y -x =2 and y + x= -2 ,Then ( x+y)(x-y)=?

We want the product of and . We’re given that , so we know we can plug in there.

We need to be careful on the other part. We’re given that , and we need to use that to find the value of . Let’s do it by multiplying each side by :

There, so now we know that and . Therefore, .