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NDA 2012
Exam
NDA
Year
2012
Subject
Mathematics
Chapter
Differentiation

NDA 2012 · Mathematics · Differentiation

Consider the following statements : 1. If y= ( x+ x) , then (d...

Consider the following statements : 1. If y=ln⁡(sec⁡x+tan⁡x)y=\ln (\sec x+\tan x), then dydx=sec⁡x\frac{d y}{d x}=\sec x. 2. If y=ln⁡(cosec⁡x−cot⁡x)y=\ln (\operatorname{cosec} x-\cot x), then dydx=cosec⁡x\frac{d y}{d x}=\operatorname{cosec} x. Which of the above is/are correct?

Options

  1. A1 only
  2. B2 only
  3. CBoth 1 and 2
  4. DNeither 1 nor 2

Correct answer

C. Both 1 and 2

Step-by-step solution

y=log⁡e(sec⁡x+tan⁡x)∴dydx=1sec⁡x+tan⁡x⋅ddx(sec⁡x+tan⁡x)\begin{aligned} & y=\log _e(\sec x+\tan x) \\ & \therefore \quad \frac{d y}{d x}=\frac{1}{\sec x+\tan x} \cdot \frac{d}{d x}(\sec x+\tan x)\end{aligned}=1sec⁡x+tan⁡x×(sec⁡x⋅tan⁡x+sec⁡2x)=(sec⁡x+tan⁡x)sec⁡x(sec⁡x+tan⁡x)=sec⁡x\begin{aligned} & =\frac{1}{\sec x+\tan x} \times\left(\sec x \cdot \tan x+\sec ^2 x\right) \\ & =\frac{(\sec x+\tan x) \sec x}{(\sec x+\tan x)}=\sec x\end{aligned}y=\log _\rho(\operatorname{cosec} x-\cot x)\frac{d y}{d x}=\frac{1}{\operatorname{cosec} x-\cot x} \cdot \frac{d}{d x}(\operatorname{cosec} x-\cot x)=1cosec⁡x−cot⁡x×(−cosec⁡x⋅cot⁡x+cosec⁡2x)=cosec⁡x(cosec⁡x−cot⁡x)(cosec⁡x−cot⁡x)=cosec⁡x\begin{aligned} & =\frac{1}{\operatorname{cosec} x-\cot x} \times\left(-\operatorname{cosec} x \cdot \cot x+\operatorname{cosec}^2 x\right) \\ & =\frac{\operatorname{cosec} x(\operatorname{cosec} x-\cot x)}{(\operatorname{cosec} x-\cot x)}=\operatorname{cosec} x\end{aligned}\therefore$ Both 1 and 2 are correct.
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