f(x.y)=f(x)+f(y),f(4)=2f(2)=2 f(8)=f(4)+f(2)=3
f(x)-f(x-2)>3 f(x)>f(x-2)+3=f(x-2)+f(8)=f(8x-16)
x>8x-16 x2
2