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provide solution for RD Sharma maths class 12 chapter Indefinite Integrals exercise 18.26 question 22

Answers (1)

Answer:
The correct answer is  x \tan (\log x)+c
Hint:

\int e^{x}\left(f(x)+f^{\prime}(x)\right) d x=e^{x} f(x)+c

Given:

\int\left[\tan (\log x)+\sec ^{2}(\log x)\right] d x

Solution:

        I=\int\left[\tan (\log x)+\sec ^{2}(\log x)\right] d x

\begin{aligned} &\text { Put } \log x=t \\ &\Rightarrow x=e^{t} \\ &d x=e^{t} d t \end{aligned}

        I=\int\left(\tan t+\sec ^{2} t\right) e^{t} d t

\begin{aligned} &\text { Here, } f(t)=\tan t \\ &f^{\prime}(t)=\sec ^{2} t \\ &\text { Let } e^{t} \tan t=p \end{aligned}

Differentiate both sides w.r.t ‘t’

        \begin{aligned} &e^{t}\left(\tan t+\sec ^{2} t\right)=\frac{d p}{d t} \\ &e^{t}\left(\tan t+\sec ^{2} t\right) d t=d p \end{aligned}

        \begin{aligned} &I=\int d p \\ &=p+c \\ &=e^{t} \tan t+c \\ &=x \tan (\log x)+c \end{aligned}

So, the correct answer is   x \tan (\log x)+c

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