Chapter 9 — Mensuration

Chapter 9 of Class 8 mathematics, 'Mensuration', teaches how to find the area, perimeter, surface area, and volume of plane figures and solid shapes including polygons, cubes, cuboids, and cylinders.

Mensuration is the branch of mathematics that deals with measurements. This chapter covers finding the area and perimeter of polygons (quadrilaterals, pentagons, hexagons) by dividing them into simpler shapes; calculating surface area of three-dimensional solids like cubes, cuboids, and cylinders; and computing volumes of these solids using cubic units. The chapter bridges 2D geometry with 3D spatial reasoning through practical examples.

1. 01Polygons can be divided into triangles and trapeziums to calculate their area
2. 02Area of trapezium = (1/2) × height × (sum of parallel sides)
3. 03Area of rhombus = (1/2) × d₁ × d₂ where d₁ and d₂ are the diagonals
4. 04Surface area of cuboid = 2(lb + bh + hl) where l, b, h are length, breadth, height
5. 05Surface area of cube = 6l² where l is the side length
6. 06Lateral surface area of cylinder = 2πrh; Total surface area = 2πr(r + h)
7. 07Volume of cuboid = length × breadth × height; Volume of cube = l³; Volume of cylinder = πr²h