2006-II-46

16-06-202112-06-2023 app.cch No Comments

Ans: B
In

Δ O B C

$\begin{array}{ll} O B = O C & (radii) \\ ∠ O C B = ∠ O B C & (base ∠ s, isos. Δ) \\ ∠ O C B = ∠ 50^{\circ} \\ ∴ ∠ A C B = 30^{\circ} \end{array}$

Hence, we have

$\begin{array}{ll} ∠ B O A = 2 \times ∠ A C B & (∠ at centre twice ∠ at ⊙^{c e}) \\ ∠ B O A = 2 \times 30^{\circ} \\ ∠ B O A = 60^{\circ} \end{array}$

2006, HKCEE, Paper 2 Properties of Circles

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