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## NCERT Class 7 Maths Textbook Chapter 14 With Answer PDF Free Download

### Chapter 14: Symmetry

#### 14.1 INTRODUCTION

Symmetry is an important geometrical concept, commonly exhibited in nature, and is used almost in every field of activity.

Artists, professionals, designers of clothing or jewelry, car manufacturers, architects, and many others make use of the idea of symmetry.

The beehives, the flowers, the tree-leaves, religious symbols, rugs, and handkerchiefs — everywhere you find symmetrical designs.

#### 14.3 ROTATIONAL SYMMETRY

What do you say when the hands of a clock go round? You say that they rotate. The hands of a clock rotate in only one direction, about a fixed point, the center of the clock-face.

Rotation, like the movement of the hands of a clock, is called a clockwise rotation; otherwise, it is said to be anticlockwise.

What can you say about the rotation of the blades of a ceiling fan? Do they rotate clockwise or anticlockwise? Or do they turn both ways?

If you spin the wheel of a bicycle, it rotates. It can rotate in either way: both clockwise and anticlockwise. Give three examples each for (i) a clockwise rotation and (ii) anticlockwise rotation.

When an object rotates, its shape and size do not change. The rotation turns an object about a fixed point. This fixed point is the center of rotation.

What is the center of rotation of the hands of a clock? Think about it. The angle of turning during rotation is called the angle of rotation. A complete turn, you know, means a rotation of 360°.

What is the degree measure of the rotation angle for (i) a half-turn? (ii) a quarter-turn? A half-turn means rotation by 180°; a quarter-turn is a rotation by 90°.

When it is 12 O’clock, the hands of a clock are together. By 3 o’clock, the minute hand would have made three complete turns; but the hour hand would have made only a quarter-turn.

What can you say about their positions at 6 O’clock?

Have you ever made a paper windmill? The Paper windmill in the picture looks symmetrical (Fig 14.11), but you do not find any line of symmetry. No folding can help you to have coincident halves.

However, if you rotate it by 90° about the fixed point, the windmill will look exactly the same. We say the windmill has rotational symmetry.

Author | NCERT |

Language | English |

No. of Pages | 12 |

PDF Size | 413 KB |

Category | Mathematics |

Source/ Credits | ncert.nic.in |

### NCERT Solutions Class 7 Maths Chapter 14 Symmetry

Q9. Give three examples of shapes with no line of symmetry.

**S olutio**

**n:**A quadrilateral, scalene triangle and a parallelogram

**Q10.** What other name can you give to the line of symmetry of –

(a) an isosceles triangle? (b) a circle?

**Solution:**

(a) Median

(b) Diameter.

**1. Draw a circle of radius 3.2 cm.**

**Solutions:**

The required circle may be drawn as follows:

Step 1: For the required radius 3.2 cm, first open the compasses.

Step 2: For the centre of a circle, mark a point ‘O’.

Step 3: Place a pointer of compasses on ‘O’.

Step 4: Now, turn the compasses slowly to draw the required circle.

NCERT Class 7 Maths Textbook Chapter 14 With Answer PDF Free Download