From the image will be a 1 = 90 (tangent circle is perpendicular to the radius shall touch point)
OA = OB, because it is the radius of a circle is the same as
isosceles triangle AOB
2 = 3 corner angle, so
= (100-180)/2
40 = angle ABC = 1 corner. A 2
40
= 90 = 130.
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