#### Answer

32 inches

#### Work Step by Step

The height and width of a television form the legs of a right triangle. The diagonal is the hypotenuse. Let d be the diagonal measurement.
$d^2=21^2+24^2$
Simplify.
$d^2=441+576$
$d^2=1017$
Take the square root of each side.
$\sqrt{d^2}=\sqrt{1017}$
Simplify and round.
$d\approx32$