Class 6 Maths Chapter 5 Understanding Elementary Shapes Exercise 5.5 pdf notes:-

**Exercise 5.5** Class 6 maths Chapter 5 Pdf Notes:-

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## Ncert Solution for Class 6 Maths Chapter 5 Understanding Elementary Shapes Exercise 5.5 Tips:-

Perpendicular Lines

When two lines intersect and the angle between them is a right angle, then the

lines are said to be perpendicular. If a line AB is perpendicular to CD, we

write AB ā„ CD .

Think, discuss and write

If AB ā„ CD , then should we say that CD ā„ ABalso?

Perpendiculars around us!

You can give plenty of examples from things around you for perpendicular

lines (or line segments). The English alphabet T is one. Is there any other

alphabet which illustrates perpendicularity?

Consider the edges of a post card. Are the edges

perpendicular?

Let AB be a line segment. Mark its mid point

as M. Let MN be a line perpendicular to AB

through M.

Does MN divide AB into two equal parts?

MN bisects AB (that is, divides AB into two

equal parts) and is also perpendicular to AB.

So we say MN is the perpendicular bisector of AB.

You will learn to construct it later.

What have we discussed?

- The distance between the end points of a line segment is its length.
- A graduated ruler and the divider are useful to compare lengths of line

segments. - When a hand of a clock moves from one position to another position we have

an example for an angle.

One full turn of the hand is 1 revolution.

A right angle is 1ā4 revolution and a straight angle is 1ā2 a revolution .

We use a protractor to measure the size of an angle in degrees.

The measure of a right angle is 90Ā° and hence that of a straight angle is 180Ā°.

An angle is acute if its measure is smaller than that of a right angle and is obtuse

if its measure is greater than that of a right angle and less than a straight angle.

A reflex angle is larger than a straight angle.

- Two intersecting lines are perpendicular if the angle between them is 90Ā°.
- The perpendicular bisector of a line segment is a perpendicular to the line

segment that divides it into two equal parts.

- Triangles can be classified as follows based on their angles:

Nature of angles in the triangle Name

Each angle is acute Acute angled triangle

One angle is a right angle Right angled triangle

One angle is obtuse Obtuse angled triangle - Triangles can be classified as follows based on the lengths of their sides:

Nature of sides in the triangle Name

All the three sides are of unequal length Scalene triangle

Any two of the sides are of equal length Isosceles triangle

All the three sides are of equal length Equilateral triangle - Polygons are named based on their sides.

Number of sides Name of the Polygon

3 Triangle

4 Quadrilateral

5 Pentagon

6 Hexagon

8 Octagon

- Quadrilaterals are further classified with reference to their properties.

Properties Name of the Quadrilateral

One pair of parallel sides Trapezium

Two pairs of parallel sides Parallelogram

Parallelogram with 4 right angles Rectangle

Parallelogram with 4 sides of equal length Rhombus

A rhombus with 4 right angles Square - We see around us many three dimensional shapes. Cubes, cuboids, spheres,

cylinders, cones, prisms and pyramids are some of them.