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Lab Manual: Algebraic Identity (a + b)^2 = a^2 + 2ab + b^2 | Lab Manuals for Class 9 PDF Download

Objective


To verify the identity (a + b)2 = a2 + 2ab + b2 by paper cutting and pasting.

Prerequisite Knowledge

  • Area of a square = (side)2.
  • Area of a rectangle = l x b.

Materials Required
A sheet of white paper, three sheets of glazed paper (different colours), a pair of scissors, gluestick and a geometry box.

Procedure


Take distinct values of a and b, say a = 4 units, b = 2 units

  • Cut a square of side a (say 4 units) on a glazed paper (blue).
  • Cut a square of side b (say 2 units) on glazed paper (pink).
  • Now, cut two rectangles of length a (4 units) and breadth b (2 units) from third glazed paper (red).
    Lab Manual: Algebraic Identity (a + b)^2 = a^2 + 2ab + b^2 | Lab Manuals for Class 9
  • Draw a square PQRS of (a+ b) = (4 + 2), 6 units on white paper sheet as shown in fig. (i).
  • Paste the squares I and II and two rectangles III and IV on the same white squared paper. Arrange all the pieces on the white square sheet in such a way that they form a square ABCD fig. (ii)
    Lab Manual: Algebraic Identity (a + b)^2 = a^2 + 2ab + b^2 | Lab Manuals for Class 9Lab Manual: Algebraic Identity (a + b)^2 = a^2 + 2ab + b^2 | Lab Manuals for Class 9

Observation

  • Area of the square PQRS on the white sheet paper.
    (a+b)2 = (4 + 2)2 = 6 x 6 = 36 sq. units ……….(i)
  • Area of two coloured squares I and II
    area of Ist square = a2 = 42 = 16 sq.units
    area of IInd square = b2 = 22 = 4 sq.units
  • Area of two coloured rectangles III and IV = 2(a x b) = 2(4 x 2) = 16 sq. units
    Now, total area of four quadrilaterals (calculated)
    = a2 + b2 + 2(ab)
    = 16 + 4 + 16
    = 36 sq. units ……….(ii)
    Area of square ABCD = Total area of four quadrilaterals = 36 sq. units
    Equating (i) and (ii)
    Area of square PQRS = Area of square ABCD
    i.e., (a+b)2 = a2 + b2 + 2ab

Result
Algebraic identity (a+b)2 = a2 + 2ab + b2 is verified.

Learning Outcome
The identity (a + b)2 = a2 + 2ab + b2 is verified by cutting and pasting of paper. This identity can be verified geometrically by taking other values of a and b.

Activity Time
Divide a square plot into four parts (quadrilaterals) such that two parts have same area and other two are squares.

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