Question

(b-c)cosA/2 = asink then k

Answer 1

Answer:

cosine rule cosA=

2bc

b

2

+c

2

−a

2

,cosB=

2ca

c

2

+a

2

−b

2

,cosC=

2ab

a

2

+b

2

−c

2

Now,2(bccosA+cacosB+abcosC)

=2(bc×

2bc

b

2

+c

2

−a

2

+ca×

2ca

c

2

+a

2

−b

2

+ab×

2ab

a

2

+b

2

−c

2

)

=2(

2

b

2

+c

2

−a

2

+

2

c

2

+a

2

−b

2

+

2

a

2

+b

2

−c

2

)

=2(

2

c

2

+a

2

+b

2

)

=a

2

+b

2

+c

2