Explanation
$$\displaystyle \int x \cos ^{-1} \left ( \frac{1-x^2}{1+x^2} \right ) dx (x > 0)$$
$$x=\tan \theta dx = \sec ^2 \theta d \theta$$
$$I=\displaystyle \int \tan \theta \cos ^{-1}(\cos 2 \theta) \sec ^2 \theta d \theta$$
$$I=\displaystyle \int 2 \theta \tan \theta \sec ^2 \theta d \theta$$
Using by parts
$$\displaystyle \int u.v \ dx=u\int v\ dx$$ $$\displaystyle -\int \left ( \dfrac{du}{dx}\int v\ dx \right )dx$$
$$I=2 \theta \displaystyle \int \tan \theta \sec ^2 \theta d \theta - \int 2 \cdot \int \tan \theta \sec ^2 \theta d \theta$$
$$=\displaystyle 2 \theta \frac{\tan ^2 \theta}{2} - 2 \times \frac{1}{2} \int \tan ^2 \theta d \theta$$
$$= \theta \tan ^2 \theta - [\int (-1+\sec ^2 \theta)d\theta]$$ ................. $$\sec^2 x=1+\tan^2 x$$
$$=\theta \tan ^2 \theta + \theta - \tan \theta +c$$
$$=\theta (1+ \tan ^2 \theta ) - \tan \theta +c$$
Replacing $$\theta $$ by $$x$$,
$$I = (\tan ^{-1}x ) ( 1+x^2) - x +c$$
$$=-x+ ( 1+x^2) \tan ^{-1}x +c$$
$$=\dfrac{1}{3}[t\Psi(t)-\int \Psi(t)dt+C].$$
$$\int {{{\tan }^{ - 1}}\left( {{{{x^3}} \over {1 + {x^2}}}} \right) + } {\tan ^{ - 1}}\left( {{{1 + {x^2}} \over {{x^3}}}} \right)dx$$
$$ = \int {{{\tan }^{ - 1}}\left[ {{{{{{x^3}} \over {1 + {x^2}}} + {{1 + {x^2}} \over {{x^3}}}} \over {1 - \left( {{{{x^3}} \over {1 + {x^2}}}} \right)\left( {{{1 + {x^2}} \over {{x^3}}}} \right)}}} \right]} dx$$
$$ = \int {{{\tan }^{ - 1}}\left( {{{{{{x^6} + {{\left( {1 + {x^2}} \right)}^2}} \over {\left( {1 + {x^2}} \right)\left( {{x^3}} \right)}}} \over 0}} \right)} dx$$
$$ = \int {{\pi \over 2}dx} $$
$$ = {\pi \over 2}x + c$$
$$ \int ( e^{\log x} + \sin x) \cos x \ dx$$ is equal to
We have,
$$I=\int{\dfrac{dx}{\sqrt{9-25{{x}^{2}}}}}$$
$$ I=\int{\dfrac{dx}{5\sqrt{\dfrac{9}{25}-{{x}^{2}}}}} $$
$$ I=\dfrac{1}{5}\int{\dfrac{dx}{\sqrt{{{\left( \dfrac{3}{5} \right)}^{2}}-{{x}^{2}}}}} $$
We know that
$$\int{\dfrac{dx}{\sqrt{{{a}^{2}}-{{x}^{2}}}}}={{\sin }^{-1}}\left( \dfrac{x}{a} \right)+C$$
Therefore,
$$ I=\dfrac{1}{5}{{\sin }^{-1}}\left( \dfrac{x}{\dfrac{3}{5}} \right)+C $$
$$ I=\dfrac{1}{5}{{\sin }^{-1}}\left( \dfrac{5x}{3} \right)+C $$
Hence, this is the correct answer.
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