Mathematics for IGCSE & O level - Pythagoras' Theorem And Trigonometry (Section 6 - No. 20)
How do you calculate the angle between two sides of a triangle if you know the lengths of all three sides?
Using the Law of Sines.
Using the Pythagorean theorem.
Using the Cosine Rule.
By finding the midpoint.
Explication
The Cosine Rule helps when all three sides are known to calculate angles.