f(x)=x^(1/2)f'(x)=1/2*x^(-1/2)=1/[2*x^(1/2)]，即x={1/[2*f'(x)]^2}=1/4*1/[f'(x)]^2由中值定理可知此时f'(ζ)=[f(9)-f(0)]/(9-0)=1/3那么ζ=1/4*1/(1/3)^2=9/4
