In any ∆ABC, (bc cos A + ca cos B + ab cos C) = A. abc B. a + b + c C. a^2 + b^2 - c^3/2 D. 1/a^2 + 1/b^2 + 1/c^2

Question

In any ∆ABC, (bc cos A + ca cos B + ab cos C) =

A. abc

B.  a + b + c

C. \(\cfrac{a^2+b^2-c^2}2\)

D. \(\cfrac1{a^2}+\cfrac1{b^2}+\cfrac{1}{c^2}\)

Answer 1

Correct option is  C. \(\cfrac{a^2+b^2-c^2}2\) 

By Cosine law,

So, ATQ

bc cos A + ca cos B + ab cos C