Law of Cosines Calculator
SSS: three sides \u2192 all three angles. SAS: two sides and the included angle \u2192 the third side (plus the other angles).
Standard notation: side a is opposite angle A, and so on.
Angle C must be the angle between sides a and b.
③ WHY IT WORKS
Why the Law of Cosines works
The Law of Cosines is the Pythagorean theorem with a correction term. In c\u00B2 = a\u00B2 + b\u00B2 \u2212 2ab\u00B7cos C, the part \u22122ab\u00B7cos C measures how the side opposite C stretches when C is obtuse (cos C is negative) or shrinks when C is acute. When C = 90\u00B0, cos C = 0 and the formula collapses back to a\u00B2 + b\u00B2 = c\u00B2.