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Q.∫cos⁡x dx=\int\cos\sqrt{x}\,dx =

(a) sin⁡x+cos⁡x+k\sin\sqrt{x} + \cos\sqrt{x} + k
(b) 12(xsin⁡x−cos⁡x)+k\frac{1}{2}(\sqrt{x}\sin\sqrt{x} - \cos\sqrt{x}) + k
(c) 2(xsin⁡x+cos⁡x)+k2(\sqrt{x}\sin\sqrt{x} + \cos\sqrt{x}) + k
(d) sin⁡x+k\sin\sqrt{x} + k
Bihar BsebBihar Board Intermediate 2026MCQ· 1mImportance★★★★★
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Put t=xt=\sqrt{x}; the integral becomes 2∫tcos⁡t dt=2(tsin⁡t+cos⁡t)+k2\int t\cos t\,dt=2(t\sin t+\cos t)+k.

Let t=xt=\sqrt{x}, so x=t2x=t^2 and dx=2t dtdx=2t\,dt. Then

∫cos⁡x dx=∫cos⁡t (2t dt)=2∫tcos⁡t dt\int\cos\sqrt{x}\,dx=\int\cos t\,(2t\,dt)=2\int t\cos t\,dt.

Integrate ∫tcos⁡t dt\int t\cos t\,dt by parts (u=t, dv=cos⁡t dtu=t,\ dv=\cos t\,dt): =tsin⁡t−∫sin⁡t dt=tsin⁡t+cos⁡t=t\sin t-\int\sin t\,dt=t\sin t+\cos t.

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