53.设f(x)在区间[2,3 ]上连续,(2,3)内可导,且 in (2,3) 时 (x)neq 0 , (2)=1, (3)=dfrac (3)(2). 证明:存-|||-f(2)=1-|||-在实数 xi in (2,3), 使得 dfrac ({S)_(f')(xi )}(f(xi ))=1.