- #1
efekwulsemmay
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Homework Statement
[tex]\int^{4}_{2} \frac{dx}{x\left(lnx\right)^{2}}[/tex]
Homework Equations
Let [tex]u=lnx[/tex]
[tex]du=\frac{1}{x}dx[/tex]
[tex]x=2 \rightarrow u=ln2[/tex]
[tex]x=4 \rightarrow u=ln4[/tex]
The Attempt at a Solution
so with the u substitution we have:
[tex]\int^{ln4}_{ln2} \frac{1}{u^{2}}du[/tex]
which goes to:
[tex]lnu^{2}\right|^{ln4}_{ln2}[/tex]
then:
[tex]2\cdot lnu\right|^{ln4}_{ln2}[/tex]
and when we work it out we get:
[tex]2\cdot\left[ln\left(ln4\right)-ln\left(ln2\right)\right][/tex]
and then:
[tex]2\cdot ln\left(\frac{ln4}{ln2}\right)[/tex]
This is where I am stuck. I am supposed to get:
[tex]\frac{1}{ln4}[/tex]
and I have no idea how they got that. Any help would be appreciated.