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Lab Manual: Algebraic Identity a^2 – b^2 = (a+b) (a-b) - Class 9 PDF Download

Objective


To verify the algebraic identity a2 – b2 = (a + b) (a - b).

Materials Required

  • Drawing sheet
  • Pencil
  • Colored papers
  • Scissors
  • Sketch pen
  • Ruler
  • Adhesive

Prerequisite Knowledge

  • Square and its area.
  • Rectangle and its area.
  • Trapezium.

Theory

  • For square and its area refer to Activity 3.
  • For rectangle and its area refer to Activity 3.
  • Trapezium is a quadrilateral whose two sides are parallel and two sides are non-parallel. In the trapezium ABCD, sides AB and CD are parallel while sides AD and BC are non-parallel.
    Lab Manual: Algebraic Identity a^2 – b^2 = (a+b) (a-b) - Class 9
  • Area of trapezium = ½ (Sum of parallel sides x Distance between parallel sides)

    = ½ (AB + CD) x DE

Procedure

  • Cut out a square WQRS of side a units from a coloured paper, (see Fig. 5.2)
    Lab Manual: Algebraic Identity a^2 – b^2 = (a+b) (a-b) - Class 9
  • Cut out a square WXYZ of side b units (b < a) from another coloured paper, (see Fig. 5.3)
    Lab Manual: Algebraic Identity a^2 – b^2 = (a+b) (a-b) - Class 9
  • Paste the smaller square WXYZ on the bigger square WQRS as shown in Fig. 5.4.
    Lab Manual: Algebraic Identity a^2 – b^2 = (a+b) (a-b) - Class 9
  • Join the points Y and R using sketch pen. (see Fig. 5.4)
  • Cut out the trapeziums XQRY and ZYRS from WQRS (see Fig. 5.5 and 5.6).
    Lab Manual: Algebraic Identity a^2 – b^2 = (a+b) (a-b) - Class 9

Lab Manual: Algebraic Identity a^2 – b^2 = (a+b) (a-b) - Class 9

  • Paste both trapeziums obtained in step 5th on the drawing sheet as shown in Fig. 5.7
    Lab Manual: Algebraic Identity a^2 – b^2 = (a+b) (a-b) - Class 9

Demonstration
From Fig. 5.2 and Fig. 5.3, we have Area of square WQRS = a2
Area of square WXYZ = b2 Now, from Fig. 5.4, we have
Area of square WQRS – Area of square WXYZ = Area of trapezium XQRY + Area of trapezium ZYRS
= Area of rectangle XQZS [from Fig. 5.7]
= XS . SZ [∴ Area of rectangle = Length x Breadth]
So, a2 – b2 = (a + b) (a – b)
Here, area is in square units.

Observation
On actual measurement, we get
a =…….. ,  b = …….. ,
So, a2 =…….. ,
b2 = …….. ,
a + b = …….. ,
a - b = …….. ,

a2 -b2 = …….. ,

and (a + b)(a - b) = …….. ,

Flence, a2 – b2 = (a + b) (a – b)

Result
The algebraic identity a2 – b2 = (a + b) (a – b) has been verified.

Application
The identity (a2 – b2) = (a + b)(a - b) can be used for

  • calculating the difference of squares of two numbers.
  • getting some products involving two numbers.
  • simplification and factorization of algebraic expressions.
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