Mathematics for IGCSE & O level - Pythagoras' Theorem And Trigonometry (Section 1 - No. 13)
Consider a triangle with sides a, b, and c, and angle A opposite side a. According to the cosine rule, what is the correct formula for side *a*?
a^2 = b^2 + c^2 - 2bc cos A
a^2 = b^2 + c^2 + 2bc cos A
a = b^2 + c^2 - 2bc cos A
a = b^2 + c^2 + 2bc cos A
Paliwanag
The correct formula is a^2 = b^2 + c^2 - 2bc cos A.