>>579
グラフを描けば分かるとおり
普通に x = 0 から x = π/4まで y = tan(x)を積分だお（´・ω・｀）

∫_{x=0 to π/4} tan(x) dx = [-log|cos(x)| ]_{x=0 to π/4} = (1/2) log(2)