Practicing Success

Target Exam

CUET

Subject

-- Mathematics - Section B1

Chapter

Differential Equations

Question:

Which one of the following is a differential equation of the family of curves $y=A e^{2 x}+B e^{-2 x}$

Options:

$\frac{d^2 y}{d x^2}-2 \frac{d y}{d x}+2 y=0$

$x \frac{d^2 y}{d x^2}+2 \frac{d y}{d x}-x y+x^2-2=0$

$\frac{d^2 y}{d x^2}=4 y$

$\left(\frac{d y}{d x}\right)^3=4 y\left(x \frac{d y}{d x}-2 y\right)$

Correct Answer:

$\frac{d^2 y}{d x^2}=4 y$

Explanation:

$y=A^{2 x}+b e^{-2 x} \Rightarrow \frac{d y}{d x}=2\left(A^{2 x}-b e^{-2 x}\right) $

$\frac{d^2 y}{d x^2}=4\left(Ae^{2 x}+b e^{-2 x}\right)=\ln y$

Hence (3) is the correct answer.