f(xy)=f(x)+f(y)
所以f(8)=f(2√2*2√2)=f(2√2)+f(2√2)=3
f(2√2)=3/2
f(2√2)=f(2)+f(√2)=3/2
f(2)=f(√2*√2)=f(√2)+f(√2)
所以f(√2)+f(√2)+f(√2)=3/2
f(√2)=1/2