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Enter the three side lengths (SSS) and recover all three interior angles using the law of cosines. Impossible side sets fail the triangle-inequality check with a clear message.
All three interior angles from three side lengths (SSS).
cos A = (b² + c² − a²) / 2bc (and cyclic)
| Symbol | Meaning |
|---|---|
| a, b, c | Side lengths |
| A, B, C | Angles opposite sides a, b, c (degrees) |
Sides 3-4-5 → angles ≈ 36.87°, 53.13°, 90°. The angles always sum to 180°.
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Side-Side-Side: all three side lengths are known, which determines the triangle's shape up to congruence.
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Content updated: September 2026