If x + y = 11 and x – y = 3, then x^2 - y^2 =  Choose the most appropriate option:  A) -4  B) 4  C) 10  D) 33  E) 40
The fastest approach has already been shown. Here's one more option.   Given:   x + y = 11   x – y = 3   Add the two equations to get: 2x = 14, which means x = 7   If x = 7, we can plug that value into either equation, to conclude that y = 4   If x = 7 and y = 4, then x² - y² = 33   Answer: 33
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If x + y = 11 and x – y = 3, then x^2 - y^2 =