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CHAPTER AT A GLANCE
Measuring Space: Perimeter and Area
•Unit: Mensuration
•Board weightage: Mensuration carries about 10 marks out of 80 in Class 9; circumference, arc length, sector area, Heron's formula and area relations are all asked (please check the latest sample paper)
•Formulas from the textbook: circumference 2πr, arc length, area of a circle, area of a sector, Heron's formula, Brahmagupta's formula for a cyclic quadrilateral, area of a trapezium and a kite
•Proofs asked: a median divides a triangle into two triangles of equal area; triangles on the same base between the same parallels
•Time to revise: about 75 minutes
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