Question

please answer question ​

Answer 1

Here,

A+B+C = 180° -------(Anglesum Property)

=> B+C=180°-A

$\sin( \frac{b + c}{2} ) = \sin( \frac{180 - a}{2} ) = \sin(90 - \frac{a}{2} ) = \cos( \frac{a}{2} )$


I hope you got it.

Answer 2

A+B+C=180 (Angle sum property)

B+C=180-A

DIVIDE BY 2

B+C/2=180-A/2

B+C/2=90 - A/2

MULTIPLY BY sin ON BOTH SIDES

sin(B+C/2)=sin(90-A/2)

sin(B+C/2)=cos A/2 (sin90-A=cosA)

All the best