奇函数f(x)=>f(0)=0,(由f(-0)=-f(0)即得)
由tana=2及万能公式有sin(2a)=2tana/(1+tana^2)=4/5
f(15sinacosa)=f(15sin(2a)/2)=f(6),
又f(x+3)=-f(x).故f(15sinacosa)=f(6)=-f(3)=f(0)=0.
奇函数f(x)=>f(0)=0,(由f(-0)=-f(0)即得)
由tana=2及万能公式有sin(2a)=2tana/(1+tana^2)=4/5
f(15sinacosa)=f(15sin(2a)/2)=f(6),
又f(x+3)=-f(x).故f(15sinacosa)=f(6)=-f(3)=f(0)=0.