If f(x) is a polynomial in x, the second derivative of f(ex) at x = 1 is : |
ef"(e) + f'(e) (f"(e) + f'(e))e2 e2f"(e) (f"(e)e + f'(e))e |
(f"(e)e + f'(e))e |
If y = f(ex) (a polynomial in ex), then $\frac{d y}{d x}=f'\left(e^x\right) . e^x$ $\Rightarrow \frac{d^2 y}{d x^2}=e^x f''\left(e^x\right) . e^x+e^x f'\left(e^x\right)$ $\Rightarrow \frac{d^2 y}{d x^2}=e^{2 x} f''\left(e^x\right)+e^x f'\left(e^x\right)$ $\left.\Rightarrow \frac{d^2 y}{d x^2}\right|_{x=1}=e^2 f''(e)+e f'(e)$ Hence (4) is correct answer. |