A3: Some important formulas of mensuration are as follows: Square -  Area -  (side)2 , Perimeter - 4 x sideTriangle - Area - ½ ( b x h ) , Perimeter - Sum of all sidesRectangle - Area - length x breadth , Perimeter - 2 * ( length + breadth )Circle - Area - πr2 , Perimeter - 2πr