Mathematics for IGCSE & O level - Pythagoras' Theorem And Trigonometry (Section 4 - No. 20)

For a triangle with sides a=5, b=8, and angle C=60 degrees, which formula is accurate for solving the length of side c?

c² = 5² + 8² - 2*5*8*cos(60)

c² = 5² + 8² + 2*5*8*cos(60)

c² = 5² - 8² - 2*5*8*cos(60)

c² = 5² - 8² + 2*5*8*cos(60)

The formula using the cosine rule to find side c is c² = a² + b² - 2ab cos C.