设f（x）是以a为周期的周期函数,证明∫a→a+lf（x）dx的值与a无关

设f（x）是以a为周期的周期函数,证明∫a→a+lf（x）dx的值与a无关
设f（x）是以a为周期的周期函数,证明∫a→a+lf（x）dx的值与a无关

设f（x）是以a为周期的周期函数,证明∫a→a+lf（x）dx的值与a无关
t = a + x,x:a->a+l,t:0->l.dt = dx.
f(t-a)=f(t).
S_{x:a->a+l}f(x)dx = S_{t:0->l}f(t-a)dt = S_{t:0->l}f(t)dt,与a无关.