How do you integrate int x e^ sqrtx dx using integration by parts?

1 Answer
Mar 17, 2016

intxe^sqrt(x)dx = 2e^sqrt(x)(x^(3/2)-3x+6sqrt(x)-6)+C

Explanation:

First, we use substitution.

Let t = sqrt(x) => dt = 1/(2sqrt(x))dx and t^3 = x^(3/2)

Then, substituting, we have

intxe^sqrt(x)dx = 2intx^(3/2)e^sqrt(x)1/(2sqrt(x))dx = 2intt^3e^tdt

Next, we apply integration by parts three times, using the formula

intudv = uv - intvdu

Integration by Parts 1:

Let u = t^3 and dv = e^tdt
Then du = 3t^2dt and v = e^t

Applying the formula:
2intt^3e^tdt = 2(t^3e^t - 3intt^2e^tdt)

Integration by Parts 2:

Focusing on the remaining integral, let u = t^2 and dv = e^tdt
Then du = 2tdt and v = e^t

Applying the formula:
intt^2e^tdt = t^2e^t - 2intte^tdt

Integration by Parts 3:

Again, focusing on the remaining integral, let u = t and dv=e^tdt
Then du = dt and v = e^t

Applying the formula:
intte^tdt = te^t-inte^tdt = te^t - e^t + C

Substituting our result into the second integration by parts step, we obtain

intt^2e^tdt = t^2e^t-2(te^t-e^t) + C = e^t(t^2-2t+2)+C

Substituting this into the first integration by parts step, we obtain

2intt^3e^tdt = 2[t^3e^t-3e^t(t^2-2t+2)]+C

=2e^t(t^3-3t^2+6t-6)+C

Finally, we substitute t=sqrt(x) back in to obtain our final result:

intxe^sqrt(x)dx = 2e^sqrt(x)(x^(3/2)-3x+6sqrt(x)-6)+C