-5 is the adjacent side, -12 is the opposite side, the hypotenuse is 13
Cos = adjacent/hypotenuse
Cos = -5/13
The answer is C.
All angles in triangle inside add up to 180
so
the angles are y, 79,37
therefor
y+79+37=180
solvde for y
y+79+37=180
add
y+116=180
subtract 116 from ot hsides
y=64
angle y=64 degrees
