设f(x)=asinx+bcosx
f(x+π)=asin(x+π)+bcos(x+π)
=-asinx-bcosx
f'(x+π)=-acosx+bsinx
代入得
asinx+bcosx+3(-acosx+bsinx)=sinx
a+3b=1
b-3a=0
a=1/10,b=3/10
f(x)=1/10sinx+3/10cosx
设f(x)=asinx+bcosx
f(x+π)=asin(x+π)+bcos(x+π)
=-asinx-bcosx
f'(x+π)=-acosx+bsinx
代入得
asinx+bcosx+3(-acosx+bsinx)=sinx
a+3b=1
b-3a=0
a=1/10,b=3/10
f(x)=1/10sinx+3/10cosx