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Provide Solution For R. D. Sharma Maths Class 12 Chapter 18  Indefinite Integrals Exercise  Revision Exercise Question 98 Maths Textbook Solution.

Answers (1)

Answer:

-\frac{1}{2} e^{-2 \log x}(2 \log x+1)+C

Hint:

You must know about integration of e?

Given:

\int \frac{\log x}{x^{3}} d x

Solution:

\int \frac{\log x}{x^{2}} \cdot \frac{1}{x} d x                    \left(p u t \log x=t, \frac{1}{x} d x=d t\right)

\int \frac{t}{e^{2 t}} d t                            \left(\log x=t, x=e^{t}\right)

\int t e^{-2 t} d t

t\left(\frac{e^{-2 t}}{-2}\right)-\int 1 \times \frac{e^{-2 t}}{-2} d t \ldots \text { using Byparts }

\left(\frac{-t e^{-2 t}}{2}\right)+\frac{1}{2}\left(\frac{e^{-2 t}}{-2}\right)

-\frac{1}{2} e^{-2 t}\left(t+\frac{1}{2}\right)+c

-\frac{1}{4} e^{-2 t}(2 t+1)+C

Resubs. t=logx,

-\frac{1}{2} e^{-2 \log x}(2 \log x+1)+C

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