Q3 of 18 Page 160

The perimeter of a circle of diameter 2 metres was measured and found to be about 6.28 metres. How do we compute the perimeter of a circle of diameter 3 metres, without measuring?

If r = radius of circle


Perimeter = Circumference of circle = 2 × π × r


When, diameter=2 m


Radius =


Perimeter = 2 × π × 1=6.28 …(eq)1


When, diameter=3 m


Radius =


Perimeter = 2 × π × 1.5=1.5 × (2 × π × 1)


= 1.5 × 6.28 …from (eq)1


= 9.42 m


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iii) What is the perimeter of an equilateral triangle with vertices on a circle of half the diameter of the first circle?

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