Question

what is the length of a diagonal of a square of side 10cm​

Answer 1

length of a diagonal =

$\sqrt{2(10 {)}^{2} }$

10root2

Answer 2

$side \: of \: square \: is10cm \\ {(diagonal})^{2} = {side}^{2} + {side }^{2} \\ let \: d \: be \: diagonal \\ {d}^{2} = 2 \times {(10)}^{2} \\ d = \sqrt{2 \times 10 \times 10} \\ d = 10 \sqrt{2} cm$

Hope it will help you....