Chapter: Pythagoras Theorem· Mathematics Part 2 (Geometry)
Answer: CD = 6, AC = \(2\sqrt{13}\)
By the theorem of geometric mean, \(CD^2 = AD \times DB = 4 \times 9 = 36\) \(\therefore CD = 6\).
In right-angled \(\Delta ADC\): \(AC^2 = AD^2 + CD^2 = 16 + 36 = 52\) \(\therefore AC = \sqrt{52} = 2\sqrt{13}\).
(Check with \(AC^2 = AD \times AB = 4 \times 13 = 52\).)