Law of Cosines Calculator
Quick answer: Enter three sides (SSS) or two sides and included angle (SAS) to solve the triangle.
Use the Law of Cosines (c² = a² + b² - 2ab·cos(C)) to solve triangles when you know all three sides (SSS) or two sides and the included angle (SAS).
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Last reviewed: April 2026Report an error
Angle A
38.21°
Angles: A=38.21°, B=60.00°, C=81.79°. Area: 17.32.
Angle A
38.21°
Angle B
60.00°
Angle C
81.79°
Area
17.32
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How to Use This Law of Cosines Calculator
- 1Enter all three sides (SSS) — OR — two sides and the included angle (SAS).
- 2Read all remaining sides, angles, and triangle area.
Frequently Asked Questions
- c² = a² + b² - 2ab·cos(C). It generalizes the Pythagorean theorem for non-right triangles. When C = 90°, cos(90°) = 0 and it reduces to a² + b² = c².
- Use Law of Cosines for SSS or SAS cases. Use Law of Sines for AAS, ASA, or SSA cases. Law of Cosines avoids the ambiguous case of SSA.
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