Answer:
45°
Explanation:
You want the acute angle in a right triangle with adjacent side 12 and hypotenuse 17.
Cosine
The cosine function relates angles and sides of a right triangle by ...
Cos = Adjacent/Hypotenuse
Application
cos(?) = 12/17
? = arccos(12/17) ≈ 45.099°
The indicated angle is about 45°.