A chord of a circle of radius 10 cm subtends an angle of $\frac{2\pi}{3}$ radians at the centre. Find the length of the chord.

Using the chord length formula: chord = 2r sin(θ/2) = 2 × 10 × sin(π/3) = 20 × (√3/2) = 10√3 cm. The angle θ/2 = π/3 = 60°, and sin 60° = √3/2. Using the full angle instead of half gives a common error.