# Chapter 9 : Areas of Parallelograms and Triangles - Ncert Solutions for Class 9 Maths CBSE

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## Chapter 9 - Areas of Parallelograms and Triangles Excercise Ex. 9.1

## Chapter 9 - Areas of Parallelograms and Triangles Excercise Ex. 9.2

We know that,

Area of parallelogram = Base corresponding attitude

Area of parallelogram ABCD = CD AE = AD CF

16 cm 8 cm = AD 10 cm

In parallelogram ABCD

AD = BC and AD || BC (Opposite sides of a parallelogram are equal and parallel)

AB = CD [Opposite sides of a parallelogram are equal]

Since HEF and parallelogram ABFH are on the same base HF and between the same parallel lines AB and HF.

area (BQC) = area (APB)

In parallelogram ABCD we find that

AB || EF (By construction) ...(1)

ABCD is a parallelogram

AB || EF and AE || BF

So, quadrilateral ABFE is a parallelogram

Now, we may observe that APB and parallelogram AB || FE are lying on the same base AB and between the same

area (PCD) = area (EFCD) ... (4)

Adding equations (3) and (4), we have

(ii)

In parallelogram ABCD we may observe that

MN || AD (By construction) ...(6)

ABCD is a parallelogram

MN || AD and AM || DN

So, quadrilateral AMND is a parallelogram

area (PCB) = area (MNCB) ... (9)

Adding equations (8) and (9), we have

On comparing equations (5) and (10), we have

Area (APD) + area (PBC) = area (APB) + area (PCD)

and also these are in between same parallel lines SR and PB.

As these lie on the same base and are between same parallel lines AS and BR

Area of PSA + Area of PAQ + Area of QRA = area of PQRS ... (1)

We know that if a parallelogram and triangle are on the same base and between the same parallels, the area of triangle is half the area of the parallelogram.

Area (PSA) + area (QRA) = area (PQRS) ... (3)

## Chapter 9 - Areas of Parallelograms and Triangles Excercise Ex. 9.3

Now the line segments BF and DE are joining two parallel lines EF and BD of same length.

So, line segments BF and DE will also be parallel to each other and also these will be equal in length.

Now as each pair of opposite sides are equal in length and parallel to each other.

Therefore BDEF is a parallelogram

We know that diagonal of a parallelogram divides it into two triangles of equal area.

Area (AFE) + area (BDF) + area (CDE) + area (DEF) = area (ABC)

DNO = BMO (By construction)

DON = BOM (Vertically opposite angles)

OD = OB (Given)

By AAS congruence rule

DON BOM

Area (DON) + area (DNC) = area (BOM) + area (BMA)

So, area (DOC) = area (AOB)

Area (DOC) = area (AOB)

Area (DCB) = area (ACB)

Now if two triangles are having same base and equal areas, these will be between same parallels

(DA || CB).

Since, BCE and BCD are lying on a common base BC and also having equal areas, so, BCE and BCD will lie between the same parallel lines.

XY || BC EY || BC

BE || AC BE || CY

So, EBCY is a parallelogram.

It is given that

XY || BC XF || BC

FC || AB FC || XB

Now parallelogram EBCY and parallelogram BCFX are on same base BC and between same parallels BC and EF

These are on same base BE and are between same parallels BE and AC

Area (ABE) = area (ACF)

the same parallels AC and BF

Let it meet the extended side CD of ABCD at point E. Join BE and AD. Let them intersect each other at O. Now portion AOB can be cut from the original field so that new shape of field will be BCE.

Now we have to prove that the area of AOB (portion that was cut so as to construct Health Centre) is equal to the area of the DEO (portion added to the field so as to make the area of new field so formed equal to the area of original field)

## CBSE Class 9 Maths Homework Help

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