此题应该是证明x>0时,f(x)为周期函数.因为x≤0时,f(x)=log2(1-x)显然不是周期函数.证:x>0时 f(x)=f(x-1)-f(x-2) =[f(x-2)-f(x-3)]-f(x-2) =-f(x-3) =-f(x-4)+f(x-5) ...