Page 174 - Start Up Mathematics_4

(b) Which closed figure has three vertices?

(i) triangle (ii) rectangle (iii) square
(c) Raghav draws a closed figure which has no edges and no corners. What figure
does Raghav draw?

(i) rectangle (ii) triangle (iii) circle
(d) Om draws a circle with a chord passing through its centre. The line touches two
points on the circumference also. What is this line called?
(i) radius (ii) arm (iii) diameter

2. Name the following parts of the given circle. M
X
(a) radii ______________ P
(b) chords ______________ C
(c) diameter ______________
(d) centre ______________ L

3. Find the diameter of the circle whose radius is given below. Y
(a) 2 cm (b) 3 cm (c) 5 cm (d) 7 cm (e) 8 cm

(f) 11 cm (g) 12 cm (h) 15 cm (i) 20 cm (j) 22 cm
4. Find the radius of the circle whose diameter is given below.
(a) 12 cm (b) 14 cm (c) 18 cm (d) 24 cm (e) 30 cm

(f) 32 cm (g) 38 cm (h) 42 cm (i) 50 cm (j) 54 cm
5. Draw three circles of different sizes using a compass and name their centre. Measure
their diameters using a scale. Then answer the following questions.

(a) What are the radii of all the circles?
(b) Is the circle with the smallest diameter the biggest circle?
(c) Is the circle with the smallest diameter the smallest circle?

Solid Shapes

Let’s revise 2D and 3D shapes.
• A shape that has only two dimensions (length and breadth or width) but no depth is
called a flat or a two-dimensional (2D) shape. Squares, triangles and rectangles are some
2D shapes.
• A shape that has three dimensions (length, breadth and depth) is called a solid or a
three-dimensional (3D) shape. Spheres, cuboids and cylinders are some 3D shapes.

Let’s now learn how to create a 3D shape from a 2D shape using a net.

Nets

A net is a two-dimensional figure that can be folded to create a three-dimensional object.
You can tell by looking at the parts of a net, what 3D figure it will create when folded.

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