getting the inner corner angle I have four points that make concave quad:

now I wanna get the inner angle of the (b) corner in degrees.
note: the inner angle is greater than 180 degree.

Draw $ac$ and use the law of cosines at $\angle b$, then subtract from $360$
$226=68+50-2\sqrt{50\cdot 68} \cos \theta \\ \cos \theta\approx -0.926 \\ \theta \approx 157.83 \\ \text{Your angle } \approx 202.17$
