Circle Theorem

• What is the rule for angles in a semicircle?

  Triangle that touches both sides should have 90
• What is the rule for an angle at a circumference?

  An angle at a circumference is half the angle at the centre
• What is the rule for angles in the same sector of a common chord?

  Angles in the same sector of a common chord are equal
• What is the rule for opposite angles in a cyclic quadrilateral?

  Opposite angles in a cyclic quadrilateral always add up to 180
• What is the rule for angles between a radius and tangent?

  The tangents at any point on the circle is perpendicular to the radius at that point, making 90
• What is alternate segment theorem?

  Angles between the chord and tangent are equal to opposite angle inside the triangle
• What is the rule for tangents to a circle from the same point?

  They will be of equal length
• What is the rule for the radius through the midpoint of a chord?

  The radius will bisect the chord at 90