1D-2D-3D-.............-nD: One dimension, say a line with LENGTH,l This is 1D as there is only one dimension - length If we want two dimensional, we need to have another dimension which is perpendicular to the previous dimension i.e., making 90 degrees with length, l. So, draw a line at one end of length that is perpendicular. So, if our previous line is horizontal, now we get a vertical line, let it be breadth,b. So, this is 2D - LENGTH and BREADTH. Examples of two dimensional figures are SQUARE, RECTANGLE, TRIANGLE, CIRCLE, etc,. Now 3D means one more dimension to be added to 2D and it should be perpendicular to length as well as breadth at that same point where length and breadth are perpendicular to each other. This is not possible to draw on a paper exactly as paper itself is a 2D object as there is only length and breadth for the paper, but for the convenience people draw a line cross to length and breadth assuming it makes 90 degrees with both of them and w...