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Explain solution RD Sharma class 12 Chapter 10 Differentiation Exercise 10.7 question 16

Answers (1)

Answer:

            \frac{d y}{d x}=\frac{1}{\sqrt{3}} \; \; \text { At }\; \; t=\frac{2 \pi}{3}

Hint:

            Use   [\tan (\pi-\theta)=-\tan \theta]   and   \frac{d(\sin t)}{d t}=\cos t

Given:

                \begin{aligned} &x=\cos t \\ &y=\sin t \end{aligned}

Solution:

x=\cos t \\

\begin{aligned} & &\frac{d x}{d t}=\frac{d \cos t}{d t}=-\sin t \end{aligned}                                                                                                               (1)

y=\sin t

\\ \frac{d y}{d t}=\frac{d \sin t}{d t} \\

\begin{aligned} & &\frac{d y}{d t}=\cos t \end{aligned}                                                                                                                                 (2)

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

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

=\frac{\cos t}{-\sin t}

\frac{d y}{d x}\; \; At\; \; \left(x=\frac{2 \pi}{3}\right)

\begin{aligned} &=-\cot \left(\frac{2 \pi}{3}\right) \\ &=-\cot \left(\pi-\frac{\pi}{3}\right) \\ &=-\left(-\cot \frac{\pi}{3}\right) \\ &=\cot \frac{\pi}{3} \end{aligned}                                                                                             

\frac{d y}{d x}\;\; At\; \; \left(x=\frac{2 \pi}{3}\right)=\frac{1}{\sqrt{3}}

Hence proved

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