Thalesâ€™s Theorem: A triangle formed by a circleâ€™s diameter and any point on the semicircle is always a right-angled triangle (the angle opposite this diameter is a right angle (90Â°)).

Sum of interior angles in triangles: Remember, the sum of interior angles in any triangle is always $180^\circ$, allowing you to solve for unknown angles by subtraction.

Using Thalesâ€™s Theorem to solve problems: Knowing that $\angle C = 90^\circ$ simplifies calculations, especially in complex diagrams with multiple triangles.

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