The lengths of two sides of an isosceles triangle are 9 cm and 20 cm. What is the perimeter of the triangle? Give reason.

Solution:

Given, the lengths of two sides of an isosceles triangle are 9 cm and 20 cm.

We have to find the perimeter of the triangle.

An isosceles triangle is a triangle that has two sides of equal length.

The third side can be either 9 cm or 20 cm.

We know that in a triangle the sum of two sides must be greater than the third side.

If the third side is 9 cm,

9 + 9 = 18 < 20

So, the third side must be 20 cm.

Perimeter of the triangle = sum of all sides

= 9 + 20 + 20

= 9 + 40

= 49 cm

Therefore, the perimeter is 49 cm.

✦ Try This: The lengths of two sides of an isosceles triangle are 8 cm and 16 cm. What is the perimeter of the triangle? Give reason.

☛ Also Check: NCERT Solutions for Class 7 Maths Chapter 6

NCERT Exemplar Class 7 Maths Chapter 6 Problem 141

The lengths of two sides of an isosceles triangle are 9 cm and 20 cm. What is the perimeter of the triangle? Give reason.

Summary:

The lengths of two sides of an isosceles triangle are 9 cm and 20 cm. The perimeter of the triangle is 49 cm.

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