It should be noted that in a circle theorem, the angle that's at the center of the circle is twice the angle at the circumference.
<h3>Circle theorem.</h3>
An overview of the circle theorem will be given as your information is incomplete. The angle that's in a semicircle is a right angle.
Also, the angles that are in the same segment are equal. Furthermore, the opposite angles that are in a cyclic quadrilateral equal 180°. The angle between the tangent and the radius is also 90°.