[" 20.A disc (of radius "rcm" ) of uniform "],[" thickness and uniform density "sigma" has "],[" a square hole with sides of length "],[ell=(r)/(sqrt(2))cm" .One corner of the hole "],[" is located at the centre of the hoxis as shown.Then the "],[" and centre of the hole lies on "y" -axis as shown.Then the "],[" and centre of position of centre of mass of disc with "],[" hole (in "cm" ) is "],[[" (a) "-(r)/(2(pi-1/4))," (b) "-(r)/(4(pi-1/4))],[" (c) "-(r)/(4(pi-1/2))," (d) "-(3r)/(4(pi-1/4))]]