I've seen this type of problem multiple times on homework, and it's confusing me like mad.
The scenario:
We have a triangle. It is a special case triangle, with one angle, one side, and another angle, in a row, known.
The sum of the two known angles is less than 90, leading one to infer that the third, unknown angle is greater than 90°. What troubles me is this:
The Law of Sines will only work correctly with acute angles, and the Law of Cosines requires two or more sides to be known, in this case one one side is known.
I am currently looking at this specific problem: angles A and B are known, respectively equaling 42° and 38°, and side c being 50, making this an ASA case.
Taking the angle measures from 180 yields 100°, the measure of angle C. Going back to the issue with the Laws of Sines and Cosines, this is an issue, considering I cannot use the Law of Sines with angles A and C, and their respective sides.
What would I do in this case to find sides a, and in turn find side b?
It works fine. $\frac c{\sin 100^\circ} \approx 50.77$.
Then $50.77 \sin 42^\circ \approx 33.97$ and $50.77 \sin 38^\circ \approx 31.26$.
Check $33.97^2+31.26^2-2\cdot 33.97\cdot 31.26 \cos 100^\circ\approx 2500=50^2$