Question

in the figure 'O' is the centre of the circle, angle ABO=20 degree and angle ACO=30 degree, where A, B, C are points on the circle. Find angle BOC
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Answer 1

oc= oa= ob(radii)  

so angleabo=angle 1 ( angle opposite to equal side are equal )

similarly angle aco= angle 2

so angle 1+ angle 2= 1/2 angle boc( double angle theorem in circles)

50+20= 1/2 angle boc  

70×2= angle boc  

140= angle boc