If x ¤ y = (x + y)^2 - (x - y)^2. Then √5 ¤ √5 =  Pick:
A) 0 B) 5 C) 10 D) 15 E) 20

Rationale: "x = √ 5 and y also = √ 5 applying the function ( √ 5 + √ 5 ) ^ 2 - ( √ 5 - √ 5 ) ^ 2 = ( 2 √ 5 ) ^ 2 - 0 = 4 x 5 = 20 . note : alternative approach is the entire function is represented as x ^ 2 - y ^ 2 = ( x + y ) ( x - y ) which can be simplified as ( x + y + x - y ) ( x + y - ( x - y ) ) = ( 2 x ) ( 2 y ) = 4 xy . substituting x = √ 5 and y = √ 5 you get the answer 20 answer is e ."
Answer: E