Maths Chapter 09: Mensuration

Class 08 Maths NCERT

We have learnt that for a closed plane figure, the perimeter is the distance around its boundary and its area is the region covered by it. We found the area and perimeter of various plane figures such as triangles, rectangles, circles, etc.

We have also learnt to find the area of pathways or borders in rectangular shapes. In this chapter, we will try to solve problems related to perimeter and area of other plane closed figures like quadrilaterals. We will also learn about surface area and volume of solids such as cube, cuboid and cylinder.

Area of a trapezium = half of the sum of the lengths of parallel sides × perpendicular distance between them.

Area of a rhombus = half the product of its diagonals.

Surface area of a solid is the sum of the areas of its faces. Surface area of:

• cuboid = 2(lb + bh + hl)
• cube = 6l²
• cylinder = 2πr(r + h)

Amount of region occupied by a solid is called its volume. Volume of:

• cuboid = l × b × h
• cube = l³
• cylinder = πr²h

Conversions

1 cm³ = 1 mL

1 L = 1000 cm³

1 m³ = 1000000 cm³ = 1000 L