Question

the length of the digonal of a square of side 12cm is

Answer 1

formula of diagonal of a square is:
$a \sqrt{2}$
Where a is length of side of square

So here length of diagonal is
$12 \sqrt{2} \: cm$
= 12 * 1.4 (approx)
= 16.8 cm

Answer 2

$12 \sqrt{2 }$