Let f(x) = ax (a > 0) be written as f(x) = f1 (x) + f2 (x) , where f1(x) is an even function and f2(x) is an odd function. Then f1(x + y) + f1(x – y) equals
(1) 2f1 (x + y) f2(x– y)
(2) 2f1 (x + y) f1(x – y)
(3) 2f1 (x) f2(y)
(4) 2f1(x) f1(y)