If x + y = 13 and x – y = 3, then x^2 - y^2 =  Choose the correct option
A) -4
B) 4
C) 10
D) 39
E) 40
The fastest approach has already been shown. Here's one more option.   Given:   x + y = 13   x – y = 3   Add the two equations to get: 2x = 16, which means x = 8   If x = 8, we can plug that value into either equation, to conclude that y = 5   If x = 8 and y = 5, then x² - y² = 39   Answer: 39
<result>D</result>
If x + y = 13 and x – y = 3, then x^2 - y^2 =