MENSURATION

1. Need for standard units.

2. Formulae for some geometrical figures.

3. Applications.

. POINT

LINE SEGMENT

How do we measure it?

The standard unit of length is meter.

The smaller units are mm, cm, dm.

1 UNIT

REGION ENCLOSED BY PLANE FIGURES

Which of the following

encloses more region?

The amount of region enclosed by any plane figure is called its AREA

Its area is 1 cm2

So area is measured in square units

Let us recall

l x b a2 ½ bh

bhπ r2

½π r2

2 (l +b) 4a

2π r

Perimeter

2r

π r

π r + 2r

Area of Rhombus

b

h

Area = bh

d1

d2

Area = ½ d1d2

h1

h2A

B

CD

Area of a general Quadrilateral

Area = ½ AC ( h1 + h2 )

B

A

CD

3cm

5cm8cm

Area = ½ x 8 x ( 3 + 5 ) = 4 x 8 = 32 cm2

a

b

h

TRAPEZIUMA quadrilateral with one pair of

opposite sides parallel

How to find the area of a trapezium ?

lengths of parallel sides -- a & b

Distance between parallel sides - h

Area of trapezium =

1/2 * (Sum of parallel sides) *Distance between them

Area = ½ * (a + b ) * h

Find the area of the given trapezium.

6 cm

10 cm

5 cm

a = 10 cm , b = 6 cm , h = 5 cm

Area = ½ * ( a + b ) * h

= 1 /2* ( 10 + 6 ) * 5 = 1/2 * ( 1 6 ) * 5

= 8 * 5 = 40 cm2

Calculate the area of the given trapezium ABCD in which AB // CD , AB = 16cm , CD = 12cm and the distance between AB & CD is 15cm

A B

CD

ASSIGNMENT