Book: RS Aggarwal & V Aggarwal - Mathematics
Chapter: 7. Areas
Subject: Mathematics - Class 9th
Q. No. 17 of CCE Questions
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The difference between the semi- perimeter and the sides of a ∆ ABC are 8cm, 7cm and 5cm respectively. The area of the triangle is –
Let the semi-perimeter be s
Let the sides of the triangle be a, b and c
It is given in the question that,
s – a = 8 …(i)
s – b = 7 …(ii)
s – c = 5 …(iii)
Now, by adding (i), (ii) and (iii) we get:
(s – a) + (s – b) + (s – c) = 8 + 7 + 5
3s – a – b – c = 20
3s – (a + b + c) = 20
We know that,
s = 
∴ 3s – 2s = 20
s = 20 cm
Now, area of the triangle = 
= 
= 20
cm2
Hence, option (c) is correct
Chapter Exercises
More Exercise Questions
cm2. Its perimeter is –
cm2. Its height is-
a2
)a
The question consists of two statements namely, Assertion (a) and Reason (R). Please select the correct answer.
Assertion (A) | Reason (R) |
Area of an equilateral triangle having each side equal to 4cm is | Area of an equilateral triangle having each side a is |
sq cm.
a2 sq units.The question consists of two statements namely, Assertion (a) and Reason (R). Please select the correct answer.
Assertion(A) | Reason (R) |
The area of an isosceles triangle having base = 8cm and each of the equal sides = 5cm is 12cm2. | The area of an isosceles triangle having each of the equal sides as a and base =b is |
.The question consists of two statements namely, Assertion (a) and Reason (R). Please select the correct answer.
Assertion(A) | Reason (R) |
The area of an equilateral triangle having side 4cm is 3cm2 | The area of an equilateral triangle having each side a is ( |
a2) sq units.The question consists of two statements namely, Assertion (a) and Reason (R). Please select the correct answer.
Assertion (A) | Reason (R) |
The sides of the triangle ABC are in the ratio 2 : 3 : 4 and its perimeter is 36 cm. Then ar(Δ ABC) = | If 2s = (a + b +c) where a, b, c are the sides of the triangle, then its area is = |
cm2.
.The question consists of two statements namely, Assertion (a) and Reason (R). Please select the correct answer.
Assertion (A) | Reason (R) |
The area of an isosceles triangle having base = 24 cm and each of the equal sides equal to 13cm is 60cm2. | If 2s = (a + b+ c) where a, b, c are the sides of a triangle, then area = |
.
cm2.Match the following columns.
Column I | Column II |
(a) The lengths of three sides of a triangle are 26 cm, 28 cm and 30cm. The height corresponding to base 28cm is……cm | (p) 6 |
(b) The area of an equilateral triangle is | (q) 4 |
(c) If the height of an equilateral triangle is | (r) 24 |
(d) Let the base of an isosceles triangle be 6 cm and each of the equal side be 5cm. Then, its height is ….cm | (s) 12 |
cm2. The perimeter of the triangle is…..cm
cm, then each side of the triangle measures …. CmThe correct answer is :
(a)-…….. (b)-……..
(c)-……… (d)-………
= 5.9]
= 3.87]
=2.454]
= 2.24]
