In a circle with centre O, AD is a diameter and AC is a chord. Point B is on AC such that OB = 7 cm and ∠OBA = 60°. If ∠DOC = 60°, then what is the length of BC?

Answer: Option C

Solution

Answer: Option C

Solution:

$$\begin{array}{rl}& OB=7\text{cm}\\ & \text{Sine Rule in }\Delta BOC\\ & \frac{OB}{\sin {30}^{\circ }}=\frac{BC}{\sin {30}^{\circ }}\\ & BC=7\text{cm}\end{array}$$