设f(x)在[a,b]上可微,且f(a)=f(b)=0,证明在(a,b)内存在一点z,使f'(z)=f(z)

Question

设f(x)在[a,b]上可微,且f(a)=f(b)=0,证明在(a,b)内存在一点z,使f'(z)=f(z)

Answer 1

令g(x)=e^(-x)f(x)
则g(a)=g(b)=0
所以存在z,使得
g'(z)=e^(-z)f'(z)-e^(-z)f(z)=0
即 f'(z)-f(z)=0
f'(z)=f(z)