f(x) 是偶函数,则 f(- x) = f(x)
f(x+2)是偶函数,则 f(- x + 2)= f(x + 2)
所以,f(x + 2) = f(- x + 2)= f[-(x - 2)] = f(x - 2) ..(1)
令 t = x - 2,则 x + 2 = t + 4
(1) 式可以写为:f(t + 4) = f(t)
所以,f(x) 的周期是 4
f(x) 是偶函数,则 f(- x) = f(x)
f(x+2)是偶函数,则 f(- x + 2)= f(x + 2)
所以,f(x + 2) = f(- x + 2)= f[-(x - 2)] = f(x - 2) ..(1)
令 t = x - 2,则 x + 2 = t + 4
(1) 式可以写为:f(t + 4) = f(t)
所以,f(x) 的周期是 4