JAMB 1991 · UME · Q32

The area of a square is $144\text{ cm}^2$ . Find the length of its diagonal.

Worked solution (try it first)

The side is $\sqrt{144} = 12$ cm.
The diagonal is the hypotenuse of a right-angled triangle with two sides of 12: $\sqrt{12^2 + 12^2} = 12\sqrt2$ cm, option C.