4. Complete Activity 2: To prove that the pairs of vertically opposite angles are equal by
cutting and pasting method on an A4 size sheet
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Objective
To verify that the opposite angles of a cyclic quadrilateral are supplementary by paper folding activity.
Materials Required
White paper sheet, compass, glazed papers, pencil, a pair of scissors, gluestick.
Procedure
Draw a circle of radius 2 cm on a white glazed paper with centre O.
Cut this circle with centre O and draw one more circle of same radius.
Take any four points A, B, C, D on the circumference of both the circles.
Join AB, BC, CD, DA by paper folding on the both the circles.
We get a cyclic quadrilateral ABCD on both the circles
Take ∠A and ∠C of blue colour and ∠B and ∠D of pink colour in both circles.
From the second circle, using transparent sheets make cut outs of ∠A, ∠B, ∠C, ∠D.
. Take ∠A and ∠C of blue colour and ∠B and ∠D of pink colour.
Make a straight line on white paper sheet. Place cut outs of ∠A and ∠C adjacent to each other on a straight line and paste them
Take cut outs of ∠B and ∠D and place them adjacent to each other on another straight line and paste them
Observation
As ∠A and ∠C forms a linear pair.
∴ ∠A + ∠C = 180°
Similarly, ∠B + ∠D = 180°
Result
Hence, it is verified that in a cyclic quadrilateral, sum of opposite angles is 180°.
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