Okay, Nomvelo, here are some key Euclidean Geometry notes and theorems from Grade 10 to 12. This is a summary, so make sure to refer to your textbook for full proofs and examples!
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Basic Angle Relationships (Grade 10)
- Angles on a straight line sum to 180°.
- Angles around a point sum to 360°.
- Vertically opposite angles are equal.
- Parallel Lines and Transversals: Corresponding angles are equal, alternate interior angles are equal, and co-interior angles sum to 180°.
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Triangle Properties (Grade 10-11)
- Sum of angles in a triangle is 180°.
- Exterior angle of a triangle equals the sum of the two opposite interior angles.
- Congruence Conditions: SSS, SAS, AAS, RHS.
- Similarity Conditions: AAA, SSS, SAS.
- Midpoint Theorem: The line segment joining the midpoints of two sides of a triangle is parallel to the third side and is half the length of the third side.
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Circle Theorems (Grade 11-12)
- The line from the center perpendicular to a chord bisects the chord.
- The angle subtended by an arc at the center is twice the angle subtended by the same arc at any point on the circumference.
- Angles subtended by the same arc (or in the same segment) are equal.
- The angle in a semicircle is 90°.
- Cyclic Quadrilateral: Opposite angles sum to 180°, and the exterior angle equals the interior opposite angle.
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Tangent Theorems (Grade 11-12)
- A tangent is perpendicular to the radius at the point of contact.
- Tangents drawn from an external point to a circle are equal in length.
- Tan-Chord Theorem: The angle between a tangent and a chord through the point of contact is equal to the angle in the alternate segment.
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Proportionality and Similarity (Grade 12)
- Proportionality Theorem (Thales' Theorem): If a line parallel to one side of a triangle intersects the other two sides, then it divides the two sides proportionally.
- Similarity in Right-Angled Triangles: If an altitude is drawn to the hypotenuse of a right-angled triangle, then the two triangles formed are similar to the original triangle and to each other.
That's 2 down. 3 left today — send the next one.