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Cosine Law Calculator

Solve triangles using the cosine law (law of cosines). Calculate unknown sides and angles, classify triangle types, and get step-by-step solutions with detailed explanations.

Cosine Law Calculator
Enter known sides and angles to solve the triangle
Current Setup:
Triangle ABC: a=?, b=?, c=?, A=?°, B=?°, C=?°
Side a is opposite angle A, side b is opposite angle B, side c is opposite angle C
Cosine Law Formulas
a2=b2+c2−2bccos⁡Aa^2 = b^2 + c^2 - 2bc\cos A
b2=a2+c2−2accos⁡Bb^2 = a^2 + c^2 - 2ac\cos B
c2=a2+b2−2abcos⁡Cc^2 = a^2 + b^2 - 2ab\cos C
When to use:
  • SAS: Two sides and the included angle
  • SSS: All three sides are known
  • Finding angles when all sides are known
Triangle Types: Acute, Right, or Obtuse based on side relationships
Related Resources
Cosine Law Applications