对所有实数x 、y ,若函数y=f(x),满足f(xy)=f(x)f(y),且f(0)不等于0,求f(2009)=( )
别人说是：
f(0) = f(0)*f(0) => f(0) = 1
f(0) = f(0) * f(2009) = f(2009) = 1
可是2009和0不是应该还要满足x和y的关系式吗?