Question

已知f(x)是周期为2的周期函数,如果f(1)=4,那么f(9)=

Answer 1

f(9)=f(7+2)=f(7)=f(5+2)=f(5)=f(3+2)=f(3)=f(1+2)=f(1)=4
或者,周期是2,则周期的整数倍（不等于0）还是周期,所以8也是周期,
所以f(9)=f(1+8)=f(1)=4