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Class 8 Textbook 2016 : Mathematics

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Meena Study Centre By- Prabhash Pratap Singh PRACTICAL GEOMETRY 57 CHAPTER Practical Geometry 4.1 Introduction You have learnt how to draw triangles in Class VII. We require three measurements (of sides and angles) to draw a unique triangle. Since three measurements were enough to draw a triangle, a natural question arises whether four measurements would be sufficient to draw a unique four sided closed figure, namely, a quadrilateral. DO THIS Take a pair of sticks of equal lengths, say 10 cm. Take another pair of sticks of equal lengths, say, 8 cm. Hinge them up suitably to get a rectangle of length 10 cm Fig 4.1 and breadth 8 cm. This rectangle has been created with the 4 available measurements. Now just push along the breadth of the rectangle. Is the new shape obtained, still a rectangle (Fig 4.2)? Observe that the rectangle has now become a parallelogram. Have you altered the Fig 4.2 lengths of the sticks? No! The measurements of sides remain the same. Give another push to the newly obtained shape in a different direction; what do you get? You again get a parallelogram, which is altogether different (Fig 4.3), yet the four measurements Fig 4.3 remain the same. This shows that 4 measurements of a quadrilateral cannot determine it uniquely. Can 5 measurements determine a quadrilateral uniquely? Let us go back to the activity! 4

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Class 8 Textbook 2016 : Mathematics
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Class 8 Textbook 2016 : Mathematics
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