Mathematics for IGCSE & O level - Pythagoras' Theorem And Trigonometry (Section 4 - No. 8)
If you know the lengths of all three sides of a triangle, which trigonometric rule is most appropriate for calculating the angles?
The Sine Rule
The Tangent Rule
The Cosine Rule
Pythagorean Theorem
Explication
The Cosine Rule is used when all three sides are known to calculate angles.