定义在非零实数集上的函数f(x)对任意非零实数x,y恒有f（xy）=f（x）+f（y）,当x

f(1)=f(1*1)=f(1)+f(1), f(1)=0.
0=f(1)=f[(-1)(-1)]=f(-1)+f(-1), f(-1)=0.
f[x^2] = f(x*x) = f(x) + f(x) = 2f(x),
2f(x)=f[x^2] = f[(-x)*(-x)] = f(-x)+f(-x) = 2f(-x),
f(-x)=f(x), f(x)为偶函数.
f(x)为偶函数,且在x>0时单调递增,所以,在x0, x>0, 8(x-2)