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∫1+x2x4dx\int \frac{\sqrt{1+x^2}}{x^4} dx is equal to :

Solution

✅ Correct Option: 2

Take xx out of the root: the integrand is 1x31+1x2\frac{1}{x^3}\sqrt{1+\frac{1}{x^2}}.

Put u=1+1x2u=1+\frac{1}{x^2}, so du=−2x3dxdu=-\frac{2}{x^3}dx.

The integral becomes −12∫u du=−13u3/2+C=−13(1+1x2)3/2+C-\frac{1}{2}\int\sqrt{u}\,du=-\frac{1}{3}u^{3/2}+C=-\frac{1}{3}\left(1+\frac{1}{x^2}\right)^{3/2}+C.

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