JAMB 2013 · UTME · Q28

Find the length of a chord which subtends an angle of $90^\circ$ at the centre of a circle whose radius is $8\text{ cm}$ .

Worked solution (try it first)

The chord and the two radii make a triangle with a right angle at the centre and two sides of 8 cm.
Pythagoras: the chord is $\sqrt{8^2 + 8^2} = \sqrt{128}$ .
$\sqrt{128} = \sqrt{64 \times 2} = 8\sqrt2$ cm, option D.