What Have We Discussed?

The circle, the square, the rectangle, the quadrilateral and the triangle are examples of planesolid figures; the cube, the cuboid, the sphere, the cylinder, the cone and the pyramid are examples of solidplane shapes.

Plane figures are examples of -D and the solid shapes are of -D.

The corners of a solid shape are called its ; the line segments of its skeleton are its ; and its flat surfaces are its .

A is a skeleton-outline of a solid that can be folded to make it.

• The same solid can have several types of nets.

Solid shapes can be drawn on a flat surface (like paper) realistically. We call this: 2-D representation of a 3-D solid.

• Two types of sketches of a solid are possible:

(a) An sketch does not have proportional lengths. Still it conveys all important aspects of the appearance of the solid.

(b) An sketch is drawn on an isometric dot paper.

In an isometric sketch of the solid the measurements kept proportional.

• Visualising solid shapes is a very useful skill. You should be able to see ‘hidden’ parts of the solid shape.

• Different sections of a solid can be viewed in many ways:

(a) One way is to view by cutting or slicing the shape, which would result in the cross-section of the solid.

(b) Another way is by observing a 2-D shadow of a 3-D shape.

(c) A third way is to look at the shape from different angles; the front-view, the side-view and the top-view can provide a lot of information about the shape observed.