Question

If angles A, B, C of a ΔABC form an increasing AP, then sin B =

(a) 1/2

(b) √3/2

(c) 1

(d) 1/√2

Answer 1

(b) In ΔABC, angles A,B,C are in A.P., 

B – A = C – B 

2B = A + C      ...(i) 

also, A + B + C = 180° (Angle sum Property) 

2 B + B = 180° 

B = 60° 

Hence, sin B = sin60° =  √3/2