5.3 The Fundamental Theorem of Calculus/31

$\int _{0}^{\frac {\pi }{4}}\sec ^{2}(t)\,dt=\tan(t){\bigg |}_{0}^{\frac {\pi }{4}}=\tan \left({\frac {\pi }{4}}\right)-\tan(0)=1-0=1$