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Find \(\int_0^1 20x^3 e^{x^4}\) dx.(a) (e-1)(b) 5(e+1)(c) 5e(d) 5(e-1)I had been asked this question during an interview.My question comes from Evaluation of Definite Integrals by Substitution in portion Integrals of Mathematics – Class 12

Answer» RIGHT option is (d) 5(e-1)

To explain I would SAY: I=\(\int_0^1 20x^3 e^{X^4}\) dx

Let x^4=t

Differentiating w.r.t x, we get

4x^3 dx=dt

∴The new limits

When x=0, t=0

When x=1,t=1

∴\(\int_0^1 \,20x^3 \,e^{x^4} \,dx=\int_0^1 5e^t dt\)

\(=5[e^t]_0^1=5(e^1-e^0)\)=5(e-1).


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