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Please Solve R.D.Sharma Class 12 Chapter 18 Indefinite Integrals Exercise  Revision Exercise Question 85 Maths Textbbok Solution.

Answers (1)

Answer:

\frac{x}{2} \sqrt{x^{2}-a^{2}}-\frac{a^{2}}{2} \log \left|x+\sqrt{x^{2}-a^{2}}\right|+c

Hint:

You must know about integration of \sqrt{x^{2}-a^{2}}

Given:

\int \sqrt{x^{2}-a^{2}} d x

Solution:

I=\int 1_{I I} \cdot \sqrt{x_{I}^{2}-a^{2}} d x

=\sqrt{x^{2}-a^{2}} \int 1 d x-\int\left(\frac{d}{d x}\left(\sqrt{x^{2}-a^{2}}\right) \int 1 d x\right) d x

=\sqrt{x^{2}-a^{2}} \cdot x-\int \frac{1 \times 2 x}{2 \sqrt{x^{2}-a^{2}}} \cdot x d x

=\sqrt{x^{2}-a^{2}} \cdot x-\int\left(\frac{x^{2}-a^{2}+a^{2}}{\sqrt{x^{2}-a^{2}}}\right) d x

=x \sqrt{x^{2}-a^{2}}-I-a^{2} \int \frac{1}{\sqrt{x^{2}-a^{2}}} d x

\therefore 2 I=x \sqrt{x^{2}-a^{2}}-a^{2} \ln \left|x+\sqrt{x^{2}-a^{2}}\right|

\Rightarrow I=\frac{x}{2} \sqrt{x^{2}-a^{2}}-\frac{a^{2}}{2} \ln \left|x+\sqrt{x^{2}-a^{2}}\right|+C

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