The length of diagonal of a square whose area is 216 cm2 is?

Area of sqaure = (side)²

⇒ 216 = (side)²

⇒ side = 6\(\sqrt {6}\) cm

diagonal of square = \(\sqrt {2}\) × side

                            = \(\sqrt {2}\) × 6\(\sqrt {6}\)

                          = 6\(\sqrt {12}\) = 12\(\sqrt {3}\) cm