Solution
= Solution
For $u>0$, the principal <inverse tangent> satisfies $\arctan u+\arctan(1/u)=\pi/2$: the two positive acute angles are complementary. Taking $u=\pi/4$ therefore makes the argument of the <natural logarithm> equal to $(2/\pi)(\pi/2)=1$. The requested value is \b[$\ln1=0$].