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E:\Working\Focus_Learning\Math_Genius_5_(05-10-2023)\Open_Files\CHAP_11
\\November 22, 2023 5:10 PM Surender Prajapati Proof 5 Reader _________________________ Date: ___________________74

perimeter of an equilateral triangle

We know that a triangle whose all three sides are of equal length is Remember
called an equilateral triangle. Always assign a
In the adjoining figure, ABC is an equilateral triangle whose sides are respective unit to
AB = BC = CA. the final answer.

Since perimeter of a triangle = sum of the lengths of its sides A
= AB + BC + CA

= AB + AB + AB (As, AB = BC = CA)
= 3 × AB

Thus, the perimeter of an equilateral triangle = 3 × side B AB = BC = CA C
example 10: Find the perimeter of an equilateral triangle whose side is 7 cm.

Solution: Perimeter of an equilateral triangle = 3 × side
= 3 × 7 cm
= 21 cm

Thus, the perimeter of the given equilateral triangle is 21 cm.
example 11: The perimeter of an equilateral triangular-shaped signboard is 96 cm. Find
the length of its side.

Solution: Given, the perimeter of an equilateral triangular-shaped signboard = 96 cm.
Since,
Perimeter of an equilateral triangle = 3 × side

3 × side = 96 cm

side = 96 = 32 cm.
3
Thus, the length of the side of the signboard is 32 cm.
practice time 11A

1. Find the perimeter of a rectangle whose
(a) length = 8 cm, breadth = 5 cm (b) length = 56 cm, breadth = 24 cm

(c) length = 4.5 m, breadth = 1.2 m (d) length = 8.2 m, breadth = 250 cm

2. Find the perimeter of a square whose side is:
(a) 6 cm (b) 7.2 cm (c) 9 m (d) 8.5 m

3. the sides of some triangles are given. Find the perimeter of the triangles.
(a) 4 cm, 5 cm and 6 cm (b) 3.8 cm, 4.5 cm and 5.7 cm

(c) 4.2 cm, 7 cm and 6.8 cm (d) 13 cm, 14 cm and 15 cm

4. Find the perimeter of the following equilateral triangle whose side is:
(a) 6 cm (b) 4.8 cm (c) 7 cm (d) 9.6 cm

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