Browse by Stream
QnA
Home
QnA
Go To Your Study Dashboard

Get Answers to all your Questions

header-bg qa
  • Home
  • School
  • Need solution for RD Sharma Maths Class 12 Chapter 10 Differentiation Excercise 10.7 Question 25

Need solution for RD Sharma Maths Class 12 Chapter 10 Differentiation Excercise 10.7 Question 25

Answers (1)

Answer:

             \frac{d y}{d x}\; {\mathrm{At}}\; \left(t=\frac{\pi}{4}\right)=1

Hint:

            Use product rule and  \frac{d y}{d x}=\frac{\frac{d y}{d \theta}}{\frac{d x}{d \theta}}

Given:

            \begin{aligned} &x=\cos t\left(3-2 \cos ^{2} t\right) \\ &y=\sin t\left(3-2 \sin ^{2} t\right) \end{aligned}

Solution:

x=\cos t\left(3-2 \cos ^{2} t\right)

\frac{d x}{d t}=\cos t \cdot \frac{d\left(3-2 \cos ^{2} t\right)}{d t}+\left(3-2 \cos ^{2} t\right) \frac{d \cos t}{d t}             [Using product rule]

\frac{d x}{d t}=\cos t[0-4 \cos t(-\sin t)]+\left(3-2 \cos ^{2} t\right) \times(-\sin t)               \quad\left[\because \frac{d(\cos \theta)}{d \theta}=-\sin \theta\right]

\frac{d x}{d t}=4 \cos ^{2} t \sin t-3 \sin t+2 \cos ^{2} t \sin t \\

=6 \cos ^{2} t \sin t-3 \sin t \\

\begin{aligned} &\frac{d x}{d t}=3 \sin t\left(2 \cos ^{2} t-1\right) \end{aligned}                                                                                             (1)

y=\sin t\left(3-2 \sin ^{2} t\right) \\

\begin{aligned} &\frac{d y}{d t}=\sin t \frac{\left(3-2 \sin ^{2} t\right)}{d t}+\left(3-2 \sin ^{2} t\right) \frac{d \sin t}{d t} \end{aligned}                                   [Using product rule]

=\sin t \times\left[\frac{d 3}{d t}-\frac{d\left(\sin ^{2} t\right)}{d t}\right]+\left(3-2 \sin ^{2} t\right) \cos t                                 \left[\because \frac{d \sin \theta}{d \theta}=\cos \theta\right]

=\sin t[0-4 \sin t \cos t]+3 \cos t-2 \sin ^{2} t \cos t \\

=-4 \sin ^{2} t \cos t+3 \cos t-2 \sin ^{2} t \cos t \\

=-6 \sin ^{2} t \cos t+3 \cos t \\

\begin{aligned} & &\therefore \frac{d y}{d t}=3 \cos t\left(-2 \sin ^{2} t+1\right) \end{aligned}                                                                                                     (2)

\because \frac{d y}{d x}=\frac{\frac{d y}{d t}}{\frac{d x}{d t}}

Put the values of   \frac{d y}{d t} \text { and } \frac{d x}{d t}  from the equation (2) and (1) respectively

\frac{d y}{d x}=\frac{3 \cos t\left(1-\sin ^{2} t\right)}{3 \sin t\left(2 \cos ^{2} t-1\right)} \\

\begin{aligned} &\frac{d y}{d x}=\cot t \frac{\left(1-2 \sin ^{2} t\right)}{\left(2 \cos ^{2} t-1\right)} \end{aligned}                                                                                               \left[\because \tan \theta=\frac{\sin \theta}{\cos \theta}\right]

\frac{d y}{d x}=\cot t \frac{\left(1-2\left(1-\cos ^{2} t\right)\right)}{\left(2 \cos ^{2} t-1\right)}                                                                      \left[\because \sin ^{2} \theta+\cos ^{2} \theta=1\right]  

\frac{d y}{d x}=\cot t \times \frac{\left(1-2+2 \cos ^{2} t\right)}{\left(2 \cos ^{2} t-1\right)} \\

=\cot t \times \frac{\left(2 \cos ^{2} t-1\right)}{\left(2 \cos ^{2} t-1\right)} \\

=\cot t \\  

\begin{aligned} & &\frac{d y}{d x}=\cot t \end{aligned}

\text { At } t=\frac{\pi}{4}, \frac{d y}{d x}=\cot \frac{\pi}{4}=1 \\

\begin{aligned} & &\frac{d y}{d x}\; {\mathrm{At}}\; \left(t=\frac{\pi}{4}\right)=1 \end{aligned}

 

Posted by

infoexpert27

View full answer

Crack CUET with india's "Best Teachers"

  • HD Video Lectures
  • Unlimited Mock Tests
  • Faculty Support
cuet_ads

Similar Questions

Trending Articles/News

anam-khan

Board Exam Time Table 2025 Live: UP Board exams from February 24; CBSE, BSEB date sheet soon
anam-khan

CBSE Date Sheet 2025 Live: Class 10, 12 board exam dates soon; syllabus, sample papers
anam-khan

Extra time in CBSE exams for students with type 1 diabetes: Kerala SHRC seeks report on plea

Latest Question