How do you evaluate the integral #int ln(x^2sqrt(4x-1))#?

1 Answer
Dec 28, 2016

By the laws of logarithms:

#=intlnx^2 + lnsqrt(4x - 1)dx#

#=intlnx^2dx + intlnsqrt(4x - 1)dx#

#=2intlnxdx+ 1/2intln(4x - 1)dx#

We let #u = 4x - 1#. Then #du = 4dx# and #dx = (du)/4#.

#=2intlnxdx + 1/2intlnu (du)/4#

#=2intlnxdx + 1/8intlnudu#

We need to integrate the natural logarithm function by parts. Let #u = lnx# and #dv = 1dx#. Then #du = 1/xdx# and #v = x#.

#int(udv) = uv - int(vdu)#

#int(lnx) = xlnx - int(x * 1/x)dx#

#int(lnx) = xlnx - x + C#

Back to the original integral.

#=2(xlnx - x) + 1/8(u lnu -u)+ C#

#=2xlnx - 2x + 1/8(4x - 1ln(4x - 1) - (4x - 1)) + C#

#=2xlnx - 2x + ((4x - 1)ln(4x - 1) - 4x + 1)/8 + C#

Hopefully this helps!