Find area of the shaded region, if side of the square ABCD is 20 cm - 

228.5 cm²

Radius of circle (r) = \(\frac{1}{2}\) × diagonal of ABCD

                             = \(\frac{1}{2}\) × 20\(\sqrt{2}\)

                             = 10\(\sqrt{2}\)

Area of shaded region = Area of circle - Area of square 

                                 = \(\pi\)(r)² - (side)²

                                 = \(\pi\)(10\(\sqrt{2}\))² - (20)²

                                 = \(\frac{4400}{7}\) - 400

                                 = \(\frac{4400\;-\;2800}{7}\)

                                 = \(\frac{1600}{7}\)

                                 = 228.5 cm²