NCERT Class 9 Solutions: Heron's Formula (Chapter 12) Exercise 12.2 Part 4

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Important formulas for polygons

Polygons Name and Areas

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Q-6 An umbrella is made by stitching 10 triangular pieces of cloth of two different colors (see Figure), each piece measuring. How much cloth of each colour is required for the umbrella?

An Umbrella


Semi perimeter of each triangle

Area of the triangular piece

Area of triangular piece

Cloth required for each colour

Q-7 A kite in the shape of a square with a diagonal and an isosceles triangle of baseeach is to be made of three different shades as shown in Figure. How much paper of each shade has been used in it?

Kite in the Shape of Square


We know that the diagonals of a square bisect each other at right angle.

Area of given kite

  • ()


Thus, (area of kite is

So, area of paper required of each shade

For the section III length of the triangle of sides

Semi perimeter of triangle

Finally, area of the triangular III piece