设f(z)=u(x,y)+iv(x,y)为解析函数,若u(x,y)=x²-y²,则f'(z)=______.

设f(z)=u(x,y)+iv(x,y)为解析函数,若u(x,y)=x²-y²,则f'(z)=______.
【正确答案】:2z