मराठी
Tamil Nadu Board of Secondary EducationSSLC (English Medium) Class 9

Types of Quadrilaterals

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Topics

Estimated time: 24 minutes
  • Introduction
  • Trapezium
  • Isosceles Trapezium
  • Parallelogram
  • Rectangle
  • Rhombus
  • Square
  • Example 1
  • Example 2
  • Example 3
  • Key Points Summary
CISCE: Class 6

Introduction

A quadrilateral is a closed figure with four sides and four angles. Based on the relationships between its sides and angles, different types of quadrilaterals exist — such as trapezium, parallelogram, rectangle, rhombus, and square.

Understanding these shapes is essential because they form the basis for most of the structures and objects we encounter daily, from rectangles and squares to the less common parallelograms and trapeziums.

CISCE: Class 6

Trapezium

Has only ONE pair of parallel sides then  ABCD is a trapezium.

Key Properties:

  • Sum of angles = 360°
  • Co-interior angles = 180° (angles on the same side of parallel lines A + D = 180° and B + C = 180°)

CISCE: Class 6

Isosceles Trapezium

Non-parallel sides are equal is called an isosceles trapezium.

Key Properties:

  • Non-parallel sides are equal:
    AD = BC
  • Base angles are equal:
    ∠A = ∠B and ∠C = ∠D

  • The diagonals are equal in length:
    AC = BD

  • The pairs of co-interior angles are supplementary:

    ∠A + ∠D = 180° and ∠B + ∠C = 180°
CISCE: Class 6

Parallelogram

Has TWO pairs of parallel sides (opposite sides face each other)

Key Properties:

  • Opposite sides are equal in length
    AB = DC and AD = BC

  • Opposite angles are equal
    A = C and B = D

  • Adjacent angles add up to 180°
    A + B = 180° and B + C = 180°
    ∠C + ∠D = 180° and ∠D+ ∠A= 180° 

  • Diagonals bisect each other (cross at their midpoints)
    OA = OC and OB = OD

CISCE: Class 6

Rectangle

ALL FOUR angles are 90° 

Key Properties:

  • All angles = 90°

  • Opposite sides are equal
    AB = DC,AD = BC

  • Opposite sides are parallel

  • Diagonals are equal in length
    AC = BD 

  • Diagonals bisect each other
    OA = OC,OB = OD

CISCE: Class 6

Rhombus

rhombus is a quadrilateral in which ALL SIDES are equal.

Key Properties:

  • All sides are equal

  • Opposite angles are equal.

  • Diagonals bisect each other at right angles (90°).

  • A parallelogram with equal adjacent sides.

CISCE: Class 6

Square

square is a quadrilateral in which ALL SIDES are equal and each angle is 90°.

Key Properties:

  • All sides are equal

  • All angles are right angles

  • Diagonals are equal and bisect each other at right angles.

CISCE: Class 6

Example 1

Isosceles trapezium ABCD with ∠B 82°. find angles A, C and D. 

Solution:
Steps:

  1. ∠A = ∠B = 82° (Base angles are equal)
    ∠C + ∠B = 180° => ∠C + 82° = 180° (Co-interior (same-side) angles on parallel lines are 180∘)
  2. ∠C = 180° − 82° = 98°
  3.  ∠D = ∠C = 98°
    ∴ ∠A = 82°, ∠C = 98° and ∠D = 98°. 
CISCE: Class 6

Example 2

Each angle of a quadrilateral equals x. Show it’s a rectangle.

Solution:
Steps:

  1. Sum of interior angles of any quadrilateral .
    .

  2. x = `"360°"/"4"`

Conclusion: x = 90 and the figure is a rectangle.

CISCE: Class 6

Example 3

Rhombus ABCD, with a diagonal = AC and ∠ DAC = 30°. Find all the angles of the rhombus.

Solution:
Steps:

  1. ∴ ∠CAB = ∠DAC = 30° (diagonals bisect the angles at the vertex.)
    ==> ∠DAB = 30° + 30° = 60° 

  2.  ∠BCD = ∠DAB = 60° (opposite angles are equal.) 

  3. ∠DAB + ∠ABC = 180° (adjacent angles are supplementary). 
    ⇒ 60° + ∠ABC = 180°
    ∠ABC = 180° − 60 = 120°
    Also, ∠ADC = ∠ABC = 120°
    ∴ Required angles are 60°, 120°, 60° and 120°
CISCE: Class 6

Key Points Summary

Quadrilateral Parallel Sides Sides Equal Angles Diagonals
Trapezium One pair Not equal Co-interior angles = 180° Not equal, don’t bisect
Isosceles Trapezium One pair Non-parallel sides equal Base angles equal Equal in length
Parallelogram Two pairs Opposite sides equal Opposite angles equal Bisect each other
Rectangle Two pairs Opposite sides equal All 90° Equal and bisect each other
Rhombus Two pairs All sides equal Opposite angles equal Bisect at 90°
Square Two pairs All sides equal All 90° Equal and bisect at 90°

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