If the sides of a triangle are known, but the angles are not, it is not possible to find the angles using just the side lengths alone. This is because, in a triangle, the side lengths do not determine the angles uniquely, a concept known as the "ambiguity of angles". To find the angles, additional information, such as the lengths of other sides or angles, or the use of trigonometry is needed.

One method that can be used to find the angles of a triangle if the side lengths are known is the Law of Cosines. This states that, given the lengths of all three sides of a triangle, the cosine of one angle can be found using the following formula:

cos(C) = (a^2 + b^2 - c^2) / 2ab

Where "a", "b", and "c" are the lengths of the sides of the triangle, and "C" is the angle opposite side "c".

Another method is Heron's formula, it allows you to calculate the area of a triangle if the sides are known. Once the area of the triangle is known, we can use the area with the sides length to find the angles by the sine formula or cosine formula.