1.

Find \(\int \frac{20x^3}{1+x^4} dx\).(a) 5 log⁡(x^4)+C(b) -5 log⁡(1+x^4)+C(c) 5 log⁡(1+x^4)+C(d) log⁡(1+x^4)+CI had been asked this question in class test.My question is taken from Methods of Integration-1 in division Integrals of Mathematics – Class 12

Answer» CORRECT ANSWER is (c) 5 log⁡(1+x^4)+C

To ELABORATE: Let 1+x^4=t

4x^3 dx=DT

∴\(\int \frac{20x^3}{1+x^4} dx=5\int \frac{dt}{t}\)

=5 log⁡t

Replacing t with 1+x^4, we get

\(\int \frac{20x^3}{1+x^4} dx=5 \,log⁡(1+x^4)+C\)


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