Question

O IS THE CENTER OF A CIRCLE ,BC IS A CHORD AND A IS ANY POINT ON THE CIRCLE .IF angle bac=a and ang obc =b find a+b.

Answer 1

∠O= 2∠A
in ΔOBC
OB = OC 
∠B=∠C
∠B+∠C+2∠A = 180°
2∠B+2∠A=180°
∠A+∠B= 90°

Answer 2

let boc=p
we have a= p/2 1 equation
but p= 180-2b
put the value of p in 1eq
we get
a= 2(90- b)/2
a= 90-b
and hence
a+b=90
I hope its the answer