Formula's: 1. (x+y)(x-y) = x^2 - y^2 2. (x + y)^2 = x^2 + 2xy + y^2 3. (x-y)^2= x^2 -2xy + y^2 Which above formula would be used by the following problems? 1. [(a+b) - (c+d)][(a+b) + (c+d)] 2. [(a+b)+c]^2