Law of Cosines — Solve SAS and SSS Triangles

c² = a² + b² − 2ab cosC. Use Law of Cosines for SAS (two sides and included angle) or SSS (all three sides).

PrecalculusCommon Core HSG-SRT.D.11F-TFVerified correct ✓

Worked examples

In triangle ABC, sides a = 6, b = 8, and the included angle C = 30°. Find side c using the Law of Cosines. Round to 4 decimal places.
Answer: 4.1063

In triangle ABC, sides a = 4, b = 3, and the included angle C = 120°. Find side c using the Law of Cosines. Round to 4 decimal places.
Answer: 6.0828

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