Mathematics for IGCSE & O level - Pythagoras' Theorem And Trigonometry (Section 1 - No. 1)
In triangle ABC, where a = 7, b = 5 and C = 60°. Find the value of c.
√49
√39
√30
√74
설명
Using Law of Cosines, c^2 = a^2 + b^2 - 2ab*cosC = 7^2 + 5^2 - 2*7*5*cos60 = 49+25 - 35 = 39.