I'm not sure if it's a right triangle, but if not then you can use side-angle-side (SAS). No wait we don't have an angle, so it must be a right triangle (has a 90° angle).
Using trig, a is the side opposite A, and c is the hypotenuse.
Therefore using SOH-CAH-TOA, sin < = O/H = opposite/hypotenuse:
So sin A = 15/17 = 0.882
[tex]So \: arcsin \: ( {sin}^{ - 1} ) \: of \: 0.882 \: = a[/tex]
A = 61.92° = 62°
