Mathematics for IGCSE & O level - Pythagoras' Theorem And Trigonometry (Section 1 - No. 34)
If a triangle has sides a = 4, b = 6, and angle C = 60 degrees, what is the length of side c (approximately)?
5.29
5.28
12
5
Explication
Use the cosine rule: c² = 4² + 6² - 2*4*6*cos(60) ; c ≈ 5.29