Which of the following is equal to the average (arithmetic mean) of (x+3)^2 and (x-3)^2?
Options:
(A) x^2
(B) x^2+2
(C) x^2 +4
(D) x^2+9
(E) x^2+4x Let's think first. Stream of consciousness:
Avg = [(x+3)^2 + (x-3)^2] / 2
Expanding and simplifying, (x^2 + 6x + 9 + x^2 - 6x + 9 ) / 2 = x^2 + 9
So, the answer is (D).