If $(x + y)^2 = 105$ and $x^2 + y^2 = 65$, what is the value of $xy$?
If (x + y)^2 = 105 and x^2 + y^2 = 65, what is the value of xy?
(x + y)^2 = 105
x^2 + 2xy + y^2 = 105
(x^2 + y^2) + 2xy = 105
(65) + 2xy = 105 subtract 65 from both sides
2xy = 40 divide both sides by 2
xy = 20
+21 
