If f(x)= a0+a1x+a2x^2+a3x^3+---------+a10x^10,where a0,a1,-----a10 are constants ,then the sum of coefficients of terms having even powers of x can be expressed as
(1) {f(2)+f(-2)}/2
(2) {f(2)-f(-1)}/2
(3) {f(1)-f(-1)}/2
(4) {f(1)+f(-1)}/2