Triangle ACD is congruent (identical to) Triangle BCD; They both have the common side, CD, and have sides of common length, AC and CB as they are both radii; As AC = CB, the angles CAB and CBA are equal also; The fact triangles ACD and BCD are congruent means AD = DB; We can use Pythagoras to find DB using CD and the radius: DB² = r² - CD² DB² = (51)² - (24)² DB² = 2601 - 576 DB² = 2025 DB = 45mm Since AD = DB, AB = 2(DB) = 2(AD) so: AB = 2(45) = 90mm
