Mathematics for IGCSE & O level - Pythagoras' Theorem And Trigonometry (Section 3 - No. 13)
If a triangle has sides of 5 cm, 7 cm, and 9 cm, which rule is the most appropriate to determine the angles?
The Sine Rule
The Cosine Rule
Pythagorean Theorem
The Tangent Rule
Explicación
Since you know all sides, you can use the Cosine Rule to find the angles.