Enter three side lengths for a valid triangle. The calculator then classifies by sides, by angles, and computes area and perimeter.

1. Enter the three sides.
2. Check that they satisfy the triangle inequality.
3. Read the combined classification and geometry values.

For sides 3, 4, and 5, the triangle is Scalene Right.

Area is 6 and the angles are approximately 36.869898°, 53.130102°, and 90°.

The angle calculation uses the law of cosines and clamps the cosine input to avoid NaN from tiny floating-point drift.

Blank, malformed, zero, and impossible side lengths are all rejected before any classification happens.