Maths Circle Geometry
- A triangle drawn from the two ends of a diameter will always make an angle of 90°
- A tangent is a line that just touches a single point on the edge of a circle. It will always make an angle of exactly 90°.
- Isosceles triangles formed by two radii don't have little 'tick' marks to remind you that they're the same - even though they are.
- A chord is any line drawn across a circle. No matter where you draw a chord, the line that cuts it in half will go through the centre, making it a diameter.
- Any triangles drawn from a chord will have the same angle where they touch the edge of the circle. Opposite sides of the chord add up to 180°
- The angle made at the centre of a circle is exactly double the angle made at the edge of the circle.
- Opposite angles of a cyclic quadrilateral add up to 180°
- The two tangents drawn from an outside point are always equal in length, so they create two congruent right angled triangles.
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