integrate sin x/cos x: it becomes - ln cos x (differentiate a ln function: f'(x)/f(x). If you differntiate -ln cos x, it becomes - f'(x)/f(x) = - -sin x/cos x = sin x/ cos x, thus integral of sin x/ cos x is - ln cos x
now you sub in the bounds (0 and pi/4 for x)
= -(ln cos pi/4 -ln cos 0)
using...