Page 222 - ICSE Math 7

(a) (b) (c) (d)

5. Guess the number of cubes in the following arrangements. (Some of the cubes may be hidden
from your view.)

(a) (b)

AT A GLANCE
¾ Some figures have two dimensions. These are also called plane figures. Square, rectangle, circle,
triangle and pentagon are some examples of 2D figures.
¾ Solid figures like cuboid, prism, cone and pyramid have 3 dimensions.

¾ The sum of the faces (F) and vertices (V) of a polyhedron is 2 more than the number of edges
(E) it has. Thus, F + V = E + 2. This is known as Euler’s formula.

¾ A flat pattern that can be folded to form a solid is called its net. In fact different nets can be
folded to form the same solid.

¾ Solid shapes can be drawn on a flat surface (paper). The depth of a solid is only an illusion. There
are two methods to draw 3D sketches.
(a) Oblique sketch: An oblique sketch need not have proportional lengths.

(b) Isometric sketch: In an isometric sketch, we show exact or proportional lengths of
the sides of the solid.

MENTAL MATHS

1. Choose the correct answer.

(a) An isometric sheet is made up of dots forming ______________.
(i) right-angled triangles (ii) equilateral triangles (iii) squares (iv) rectangles
(b) The number of edges in a polyhedron having 8 faces and 12 vertices is ______________.

(i) 14 (ii) 16 (iii) 18 (iv) 20
(c) Which of the following is the top view of the solid shown in the given figure?

(i) (ii) (iii) (iv)

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