Answer: C
In triangle ABD: BD = 2 × OD = 2 × 2.5 cm = 5 cm AB = 4 cm ∴ \(AD^2 = BD^2 - AB^2 = 5^2 - 4^2 = 25 - 16 = 9\) ∴ \(AD = \sqrt{9} = 3\) cm ∴ BC = AD = 3 cm
In triangle ABD: BD = 2 × OD = 2 × 2.5 cm = 5 cm AB = 4 cm ∴ \(AD^2 = BD^2 - AB^2 = 5^2 - 4^2 = 25 - 16 = 9\) ∴ \(AD = \sqrt{9} = 3\) cm ∴ BC = AD = 3 cm