Original Problem:

$\displaystyle

\int_{0}^{1}{4}/{(1+x^2)}dx

$

So I got tan^(-1)x ] 0 to 1<-- supposed to be inverse tanx evaluated from 0 to 1.

Inverse tan of 1 is pi/4 minus inverse tan of 0 is 0, so I end up with pi/4 as the answer. The book says the answer is pi... What am I doing wrong?