- #1
sooyong94
- 173
- 2
Homework Statement
I was asked to prove the integral
##\int_{\frac{4}{5}}^{1} \textrm{arcsech}(x) =2\arctan 2-\frac{\pi}{2}-\frac{4}{5} \ln 2##
Homework Equations
Integration by parts
The Attempt at a Solution
Let ##u=\textrm{arcsech} (x)##
##\textrm{sech u}=x##
##\textrm{cosh u}=\frac{1}{x}##
Differentiating implicitly,
##\textrm{sinh u} \frac{du}{dx}=\frac{-1}{x^{2}}##
##\frac{du}{dx}=\frac{-1}{x^{2}\textrm{sinh u}}##
Then I simplify it into
##\frac{-1}{x\sqrt{1-x^{2}}}##
Let ##\frac{dv}{dx}=1##
##v=x##
Using integration by parts and evaluating the integral, I got
##\frac{\pi}{2}-\sin^{-1} \frac{4}{5} -\frac{4}{5} \ln 2##
Which is numerically correct. But how do I obtain ##2\tan^{-1} 2 ## as shown in the question above?