Circle Theorems Calculator
Angles in a Semicircle
Any angle inscribed in a semicircle is a right angle (90°).
90°
Angles in Same Segment
Angles in the same segment of a circle are equal.
45°
Cyclic Quadrilateral
Opposite angles in a cyclic quadrilateral add up to 180°.
60°
Tangent-Radius Theorem
A tangent to a circle is perpendicular to the radius at the point of contact.
90°
Alternate Segment Theorem
The angle between a tangent and a chord is equal to the angle in the alternate segment.
45°
Circle
Angles
Lines
Select a Theorem
Click on a theorem to see its visualization and detailed explanation.