To find the value of an angle (let's call it angle A) in a triangle when the three sides are known, you can use the Law of Cosines, which states that:
a^2 = b^2 + c^2 - 2bc cos(A)
where a, b, and c are the side lengths of the triangle, and A is the angle opposite side a.
To solve for angle A, you can rearrange the equation to get:
cos(A) = (b^2 + c^2 - a^2) / 2bc
Then, you can take the inverse cosine (cos^-1) of both sides to get:
A = cos^-1[(b^2 + c^2 - a^2) / 2bc]
Once you have found the value of angle A, you can use the fact that the sum of the angles in a triangle is always 180 degrees to find the values of the other angles.