(Q7)If A,B and C are interior angles of triangle ABC ,then show that sin
B+C
2
=cos
A
2

Answer:

Given A,B and C are angles of triangle ABC then A+B+C=°

On dividing the above equation by 2 on both sides,we get

A
2
+
B+C
2
=°
B+C
2
=°-
A
2

on taking sin ratio on both sides

sin
B+C
2
=sin [°-
A
2
]
sin
B+C
2
=
A
2