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Q.Integrate cos⁡−1(xa+x)\cos^{-1}\sqrt{\left(\dfrac{x}{a+x}\right)} with respect to xx.

Rajasthan RbseRajasthan Board Senior Secondary Examination 2020Subjective· 3mImportance★★★★★
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Integrate by parts, taking u=cos⁡−1x/(a+x)u=\cos^{-1}\sqrt{x/(a+x)} and dv=dxdv=dx; the resulting integral simplifies with the substitution x=t2x=t^2.

Let u=cos⁡−1xa+xu=\cos^{-1}\sqrt{\dfrac{x}{a+x}}, dv=dxdv=dx, so v=xv=x.

Differentiating uu: since 1−xa+x=aa+x1-\dfrac{x}{a+x}=\dfrac{a}{a+x}, one finds after simplification

dudx=−a2x (a+x)\dfrac{du}{dx} = -\dfrac{\sqrt a}{2\sqrt x\,(a+x)}

By parts:

∫u dv=uv−∫v du=xcos⁡−1xa+x+a2∫xa+xdx\int u\,dv = uv-\int v\,du = x\cos^{-1}\sqrt{\dfrac{x}{a+x}} + \dfrac{\sqrt a}{2}\int\dfrac{\sqrt x}{a+x}dx

For I2=∫xa+xdxI_2=\displaystyle\int\dfrac{\sqrt x}{a+x}dx, substitute x=t2x=t^2, dx=2t dtdx=2t\,dt:

I2=∫t⋅2ta+t2dt=2∫(1−aa+t2)dt=2t−2atan⁡−1ta=2x−2atan⁡−1xaI_2 = \int\dfrac{t\cdot2t}{a+t^2}dt = 2\int\left(1-\dfrac{a}{a+t^2}\right)dt = 2t-2\sqrt a\tan^{-1}\dfrac{t}{\sqrt a} = 2\sqrt x-2\sqrt a\tan^{-1}\sqrt{\dfrac xa}

So: …

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