Practicing Success

Target Exam

CUET

Subject

-- Mathematics - Section B1

Chapter

Differential Equations

Question:

If y = \( { \left(\frac{1}{x}\right) }^{x} \), then \(\frac{d^2y}{dx^2}\)

Options:

x-x (1 + log x)2 – x-(x+1)

x-x (1 + log x)2 – x-(x-1)

x-x (1 + log x)-2 – x-(x+1)

x-x (1 + log x)-2 – x-(x-1)

Correct Answer:

x-x (1 + log x)2 – x-(x+1)

Explanation:

$y=(\frac{1}{x})^x⇒y=x^{-x}$

∴ log y = -x log x

$⇒ \frac{1}{y}\frac{dy}{dx}=\frac{-x}{x}+log x(-1)=-1-logx$

$\frac{dy}{dx}=y-(1+logx)$

$\frac{d^2y}{dx^2}=-y[\frac{1}{x}]-(1+logx)\frac{dy}{dx}$

$⇒-x^{-x-1}+x^{-x}(1+logx)^2=x^{-x}(1+logx)^2-x^{-x-1}$

Option A is correct.