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Explain solution RD Sharma class 12 chapter 10 Differentiation exercise Multiple choice question 20 maths

Answers (1)

Answer:

        2

Hint:

        Differentiate the function w.r.t \cos ^{-1}x

Given:

        \cos ^{-1}(2x^{2}-1)  With respect to \cos ^{-1}x

Solution:  

        \begin{aligned} &u=\cos ^{-1}\left(2 x^{2}-1\right) \\\\ &x=\cos \theta \\\\ &\theta=\cos ^{-1} x \\\\ &\frac{d \theta}{d x}=\frac{-1}{\sqrt{1-x^{2}}} \end{aligned}

        \begin{aligned} &u=\cos ^{-1}(\cos 2 \theta) \\\\ &u=2 \theta \\\\ &\frac{d u}{d x}=2 \frac{d \theta}{d x} \\\\ &\frac{d u}{d x}=\frac{-2}{\sqrt{1-x^{2}}} \end{aligned}    ...............(1)

        \begin{aligned} &v=\cos ^{-1} x \\\\ &v=\cos ^{-1}(\cos \theta), v=\theta \\\\ &\frac{d v}{d x}=\frac{d \theta}{d x} \\\\ &\frac{d v}{d x}=\frac{-1}{\sqrt{1-x^{2}}} \end{aligned}   ..................(2)

Divide (1) by (2)

        \begin{aligned} &\frac{d u}{d x}=\frac{-2}{\frac{d v}{d x}}{\sqrt{1-x^{2}}} \times \frac{\sqrt{1-x^{2}}}{-1} \\\\ &\frac{d u}{d v}=2 \end{aligned}

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