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)