If y=79e^5x+85e^-5x, then :

The correct answer is Option (4) → $\frac{d^2y}{dx^2}=25y$

$y=79e^{5x}+85e^{-5x}$

$\frac{dy}{dx}=5(79e^{5x}-85e^{-5x})$

$\frac{d^2y}{dx^2}=5×5(79e^{5x}-85e^{-5x})$

$=25(79e^{5x}-85e^{-5x})$

$\frac{d^2y}{dx^2}=25y$