Question

In$\triangle A B C$ if $2 ( b c \cos A + c a \cos B + a b \cos C ) =$

• A. 0
• B. $a + b + c$
• C. $a ^ { 2 } + b ^ { 2 } + c ^ { 2 }$
• D. None of these

Answer 1

Answer: (C)

$a ^ { 2 } + b ^ { 2 } + c ^ { 2 }$

Answer 2

On putting the values of $\cos A , \cos B$and $\cos C$, we get the required result i.e., $a ^ { 2 } + b ^ { 2 } + c ^ { 2 }$.