How do you find the integral of sqrt (t)*ln (t) dttln(t)dt?

1 Answer
Sep 4, 2015

use integration by parts to find intsqrt(t)ln(t)dt=2/3t^(3/2)(ln(t)-2/3)+Ctln(t)dt=23t32(ln(t)23)+C

Explanation:

We use integration by parts by noting that sqrt(t)=d/dt(2/3t^(3/2))t=ddt(23t32).
Therefore
intsqrt(t)ln(t)dt=2/3intln(t)d(t^(3/2))=2/3(ln(t)t^(3/2)-intt^(3/2)dln(t))tln(t)dt=23ln(t)d(t32)=23(ln(t)t32t32dln(t)).
Since d/dt(ln(t))=1/tddt(ln(t))=1t this gives
intsqrt(t)ln(t)dt=2/3(ln(t)t^(3/2)-intt^(3/2)/tdt)=2/3(ln(t)t^(3/2)-intt^(1/2)dt)=2/3(ln(t)t^(3/2)-2/3t^(3/2))+C=2/3t^(3/2)(ln(t)-2/3)+Ctln(t)dt=23(ln(t)t32t32tdt)=23(ln(t)t32t12dt)=23(ln(t)t3223t32)+C=23t32(ln(t)23)+C
With C the integration constant.