CIRCLES

We need to show that BOA + APB = 180,

In quadrilateral OAPB,

BOA + APB + OAP + OBP = 360

But OAP = OBP = 90        ...................... since the radius at the point of contact of a tangent is perpendicular to

                                                                            the tangent at the point of contact. 

BOA + APB + 90 + 90 = 360

BOA + APB = 180

Regards,

Team,

TopperLearning.