If x+y=r and x-y=s, in terms of x and y, what is r^2-s^2? Please show step by step. Thanks.
Let’s do this two ways. First, with substitution. If 
and 
, then we can rewrite 
as 
. Then we can simplify that:
The other way to go is to plug in. Say 
and 
. That makes 
and 
. Now you’re looking for 
. Which answer choice gives you 24 when you plug in and ? 
does: 
.