Heron’s Formula Class 9 Maths Ncert

We provide you with the ncert solutions of class 9 chapter 12 Herons Formula to help you out with the solutions. We are providing you with solutions for every exercise to help you with the tips and tricks to solve many questions. Here we have given NCERT Solutions for Class 9 Maths Chapter 12 Heron’s Formula.

NCERT Solutions for Class 9 Maths Chapter 12 Heron’s Formula Ex 12.1

Ex 12.1 Class 9 Maths Question 1.
A traffic signal board indicating ‘SCHOOL AHEAD’ is an equilateral triangle with side a. Find the area of the signal board using Heron’s formula. If its perimeter is 180 cm, what will be the area of the signal board?
Solution:
Let each side of the equilateral triangle be a.
Semi-perimeter of the triangle,

Ex 12.1 Class 9 Maths Question 2.
The triangular side walls of a flyover have been used for advertisements. The sides of the walls are 122 m, 22 m, and 120 m (see figure). The advertisements yield an earning of ₹5000 per m² per year. A company hired one of its walls for 3 months. How much rent did it pay?

Solution:
Let the sides of the triangular will be
a = 122m, b = 12cm, c = 22m
Semi-perimeter, s = a+b+c2
(122+120+224)m = 2642 m = 132m
The area of the triangular side wall

Rent for 1 year (i.e. 12 months) per m² = Rs. 5000
∴ Rent for 3 months per m² = Rs. 5000 x 312
= Rent for 3 months for 1320 m² = Rs. 5000 x 312 x 1320 = Rs. 16,50,000.

Ex 12.1 Class 9 Maths Question 3.
There is a slide in a park. One of its side Companies hired one of its walls for 3 months. walls have been painted in some color with the message “KEEP THE PARK GREEN AND CLEAN” (see figure). If the sides of the wall are 15 m, 11 m, and 6m, find the area painted in color.

Solution:
Let the sides of the wall be
a = 15m, b = 11m, c = 6m
Semi-perimeter,

Thus, the required area painted in color
= 20√2 m²

Ex 12.1 Class 9 Maths Question 6.
An isosceles triangle has a perimeter of 30 cm, and each of the equal sides is 12 cm. Find the area of the triangle.
Solution:
Let the sides of an isosceles triangle be
a = 12cm, b = 12cm,c = x cm
Since perimeter of the triangle = 30 cm
∴ 12cm + 12cm + x cm = 30 cm
⇒ x = (30 – 24) = 6
Now, semi-perimeter, s = 302cm =15 cm

Thus, the required area of the triangle = 9√15 cm²

NCERT Solutions for Class 9 Maths Chapter 12 Heron’s Formula Ex 12.2

Ex 12.2 Class 9 Maths Question 1.
A park, in the shape of a quadrilateral ABCD, has ∠C = 90°, AB = 9m,BC = 12m,CD = 5m and AD = 8 m.
How much area does it occupy?
Solution:
Given, a quadrilateral ABCD with ZC = 90°, AB = 9 m, BC = 12 m, CD = 5 m and AD = 8 m.
Let us join B and D, such that ABCD is a right-angled triangle.

Now, to find the area of ∆ABD, we need the length of BD.
In right-angled ∆BCD, by Pythagoras’ theorem
BD² = 50² + CD²
⇒ BD² = 12² + 5²
⇒ BD² = 144 + 25 = 169
⇒ BD = 13 m
Now, for ∆ABD, we have
a = AB = 9 m, b = AD = 8 m, c = BD = 13 m

∴ Area of quadrilateral ABCD = area of ∆BCD + area of ∆ABD = 30 m² + 35.5 m²
= 65.5 m² (approx.)

Ex 12.2 Class 9 Maths Question 2.
Find the area of a quadrilateral ABCD in which AB = 3 cm, BC = 4 cm, CD = 4 cm, DA = 5 cm and AC = 5 cm.

Solution:
Given a quadrilateral ABCD with AB = 3 cm, BC = 4 cm, CD = 4 cm, DA = 5 cm and AC = 5 cm.

For ∆ABC, a = AB = 3 cm, b = BC = 4 cm and c = AC = 5 cm

Now, area of quadrilateral ABCD = area of ∆ABC + area of ∆ACD
= 6 cm² + 9.2 cm² = 15.2 cm² (approx.)

For surface II:
It is a rectangle with length 6.5 cm and breadth 1 cm.
∴ Area of surface II = Length x Breadth
= (6.5 x 1) cm² = 6.5 cm²
or surface III:

It is a trapezium whose parallel sides are 1 cm and 2 cm as shown in the figure given below:

For surface IV and V:
Surface V is a right-angled triangle with base 6cm arid height 1.5 cm.
Also, area of surface IV = area of surface V
= 12 x base x height
= (12 x 6 x 15) cm² = 4.5 cm²
Thus, the total area of the paper used = (area of surface I) + (area of surface II) + (area of surface III) + (area of surface IV) + (area of surface V) = [2.475 + 6.5 + 1.3 + 4.5 + 4.5] cm²
= 19.275 cm²
= 19.3 cm² (approx.)

Ex 12.2 Class 9 Maths Question 4.
A triangle and a parallelogram have the same base and the same area. If the sides of the triangle are 26 cm, 28 cm and 30 cm, and the parallelogram stands on the base 28 cm, find the height of the parallelogram
Solution:
For the given triangle, we have a = 28 cm, b = 30 cm, c = 26 cm

Area of the given parallelogram = Area of the given triangle
∴ Area of the parallelogram = 336 cm²
⇒ base x height = 336
⇒ 28 x h = 336, where ‘h’ is the parallelogram’s height.
⇒ h = 33628 = 12
Thus, the required height of the parallelogram = 12 cm

Ex 12.2 Class 9 Maths Question 5.
A rhombus shaped field has green grass for 18 cows to graze. If each side of the rhombus is 30 m and its longer diagonal is 48 m, how much area of grass field will each cow be getting?
Solution:
Here, each side of the rhombus = 30 m.
Let ABCD be the given rhombus and the diagonal, BD = 48 m

Since a diagonal divides the rhombus into two congruent triangles.
∴ Area of triangle II = 432 m²
Now, the total area of the rhombus = Area of triangle I + Area of triangle II
= 432 m² + 432 m²= 864 m²
Area of grass for 18 cows to graze = 864 m²
⇒ Area of grass for 1 cow to graze = 86418 m²
= 48 m²

Ex 12.2 Class 9 Maths Question 6.
An umbrella is made by stitching 10 triangular pieces of cloth of two different colours (see figure), each piece measuring 20 cm, 50 cm and 50 cm. How much cloth of each colour is required for the umbrella?

Ex 12.2 Class 9 Maths Question 7.
A kite in the shape of a square with a diagonal 32 cm and an isosceles triangle of base 8 cm and sides 6 cm each is to be made of three different shades as shown in figure. How much paper of each shade has been used in it?

Solution:
Each shade of the paper is divided into 3 triangles i.e., I, II, III

8 cm
For triangle I:
ABCD is a square [Given] ∵ Diagonals of a square are equal and bisect each other.
∴ AC = BD = 32 cm
Height of AABD = OA = (12 x 32 )cm
= 16 cm
Area of triangle I = (12 x 32 x 16 ) cm²
= 256cm²

For triangle II:
Since the diagonal of a square divides it into two congruent triangles.
So, area of triangle II = area of the triangle I
∴ Area of triangle II = 256 cm²

For triangle III:
The sides are given as a = 8 cm, b = 6 cm and c = 6 cm

Thus, the area of different shades are:
Area of shade I = 256 cm²
Area of shade II = 256 cm²
and area of shade III = 17.92 cm²

Ex 12.2 Class 9 Maths Question 8.
A floral design on a floor is made up of 16 triangular tiles, the sides of the triangle being 9 cm, 28 cm and 35 cm (see figure). Find the cost of polishing the tiles at the rate of 50 paise per cm .

Solution:
Let the sides of the triangle be a = 9 cm, b = 28 cm, c = 35 cm

Total area of all the 16 triangles = (16 x 88.2) cm² = 1411.2 cm² (approx.)
Cost of polishing the tiles = Rs. 0.5 per cm²
∴ Cost of polishing all the tiles = Rs. (0.5 x 1411.2) = Rs. 705.60 (approx.)

Ex 12.2 Class 9 Maths Question 9.
A field is in the shape of a trapezium whose parallel sides are 25 m and 10 m. The non-parallel sides are 14 m and 13 m. Find the area of the field.
Solution:
Let the given field is in the form of a trapezium ABCD such that parallel sides are AB = 10 m and DC = 25 m
Non-parallel sides are AD = 13 m and BC = 14 m.
We draw BE || AD, such that BE = 13 m.

The given field is divided into two shapes (i) ∆BCE, (ii) parallelogram ABED For ∆BCE:
Sides of the triangle are a = 13 m, b = 14 m, c = 15 m

(ii) For parallelogram ABED:
Let the height of the ∆BCE corresponding to the side EC be h m.
Area of a triangle = 12 x base x height
∴ 12 x 15 x h = 84
⇒ (10 + 82×215 = 565
Now, the area of a parallelogram = base x height
= (10 x 565) = (2 x 56) m² = 112 m²
So, the area of the field
= area of ∆BCE + area of parallelogram ABED
= 84 m² + 112 m² = 196 m²

Conclusion

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