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Provide Solution For R.D.Sharma Maths Class 12 Chapter 10 Differentiation Exercise 10.3  Question 16 Maths Textbook Solution.

Answers (1)

Answer:  \frac{dy}{dx}=\frac{4}{1+4x^{2}}

Hint:

\begin{aligned} &\frac{d}{d x}(\text { constants })=0 \\ &\frac{d}{d x}\left(x^{n}\right)=n x^{n-1} \end{aligned}

Given:

\begin{aligned} &\tan ^{-1}\left\{\frac{4 x}{1-4 x^{2}}\right\} \\ &\frac{-1}{2}<x<\frac{1}{2} \end{aligned}

Solution:

Let,

y=\tan ^{-1}\left\{\frac{4 x}{1-4 x^{2}}\right\}

Let,

2x=\tan \theta

\theta =\tan ^{-1}2x

y =\tan ^{-1}\left \{ \frac{2\tan \theta }{1-\tan ^{2}\theta } \right \}

Using \tan 2\theta =\frac{2\tan \theta }{1-\tan ^{2}\theta }

y=\tan ^{-1}\left ( \tan 2\theta \right )

Considering the limits,

\begin{aligned} &\frac{-1}{2}<x<\frac{1}{2} \\ &-1<2 x<1 \\ &-1<\tan \theta<1 \\ &-\frac{\pi}{4}<\theta<\frac{\pi}{4} \\ &-\frac{\pi}{2}<2 \theta<\frac{\pi}{2} \end{aligned}                       \left \{ \tan 45^{\circ}=1 \right \}

Now,

y=\tan ^{-1}\left ( \tan 2\theta \right )

y=2\theta                                                            

y=2\tan ^{-1}\left ( 2x \right )                                                        \left [ since,2x=\tan \theta \right ]

Differentiating with respect to x , We get

\begin{aligned} &\frac{d y}{d x}=\frac{d}{d x}\left(2 \tan ^{-1} 2 x\right) \\ &\frac{d y}{d x}=2 \times \frac{2}{1+(2 x)^{2}} \\ &\frac{d y}{d x}=\frac{4}{1+4 x^{2}} \end{aligned}                            \frac{d\left ( tan^{-1}x \right )}{dx}=\frac{1}{1+x^{2}}

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