Find the angle α as shown in the triangle below

Question

One side is 25, the other side is 20 and the other side is 18. The angle α is between sides with length 25 and 18.

Answer 1

You can use the law of cosines on this:

20² = 18² + 25² - 2(18)(25)cos(α).

Solve for cos(α) and take inverse cosine.