【無字證明】反三角函數 2022-08-132022-08-13 by ejsoon \frac\pi4=arctan\frac12+arctan\frac13 \frac\pi4=arctan2-arctan\frac13 \frac\pi4=arctan3-arctan\frac12 \frac\pi2=arctan\frac11+arctan\frac12+arctan\frac13 \pi=arctan1+arctan2+arctan3
