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Perimeter of a triangle

In the given figure, ABC is a triangle in which AB, BC and CA
are its sides.

Perimeter of DABC = AB + BC + CA
Perimeter of a triangle = Sum of all its sides

example 9. Find the perimeter of a triangle whose sides are
5 cm, 7 cm and 8 cm respectively.

Solution. Perimeter of the triangle = Sum of all its sides

= (5 + 7 + 8) cm

= 20 cm

example 10. If the perimeter of a triangle is 42 cm and two of its sides are 12 cm and
15 cm respectively, find the length of the third side.

Solution. Perimeter of the triangle = Sum of its all sides

42 = 12 + 15 + third side 12 cm 15 cm

42 = 27 + third side

So, the third side = 42 – 27

= 15 cm. ?
Perimeter = 42 cm
Hence, the length of the third side is 15 cm.

Exercise 8A

1. identify which of these shapes has the largest perimeter. each small square measures
1 cm.

1 cm
a. b. c.

192 Mathematics 5