Chapter 6: Perimeter and Area
Perimeter tells us how far it is all the way around a shape; area tells us how much space it covers. In this chapter we revise the formulas for rectangles, squares and triangles, and use them to solve real problems like fencing a garden or tiling a floor.
In this chapter you will
- find the perimeter of rectangles, squares, triangles and regular polygons
- find the area of rectangles and squares, and of shapes split into rectangles
- estimate area using squared paper
- find the area of a triangle as half of a rectangle
- see that the same area can have different perimeters
Topics
- Perimeter NCERT 6.1
Perimeter of a polygon = sum of all its sides.
- Area NCERT 6.2
Area is the amount of region a closed shape covers. It is measured in square units (sq cm, sq m).
- Area of a Triangle NCERT 6.3
A diagonal cuts a rectangle into two equal triangles.
Key words
- Perimeter
- the distance all the way around a closed shape
- Polygon
- a closed shape made of straight line segments
- Area
- the amount of region a closed shape covers
- Square unit
- a square with sides of 1 unit (for example 1 sq cm)
- Diagonal
- a line from one corner to the opposite corner
- Base and height
- the bottom side of a triangle, and the straight-up distance to its top point
Summary
- Perimeter is the distance all the way round a shape: add up the lengths of its sides.
- Rectangle: perimeter = 2 × (length + breadth). Square: perimeter = 4 × side.
- Area is how much flat space a shape covers, counted in unit squares (sq cm, sq m).
- Rectangle: area = length × breadth. Square: area = side × side. Triangle: area = ½ × base × height.
- Shapes with the same area can have different perimeters, and shapes with the same perimeter can have different areas.