It we measure the circumference and diameter of various circles; we will find that the ration of circumference and their corresponding diameters, is always constant. This constant ratio is denoted by Greek letter . The value of is 22/7or 3.1415.
Or (, being radius)
The sum of two radii of two circles is 7cm and the difference of their circumference is 8 cm. Find the two circumferences.
Let be the radius of one circle.
The radius of the other circle cm
Now, circumference of circle with radius cm cm --- (1)
and, circumference of circle with radius cm --- (2)
The difference of two circumference = 8 cm --- (3)
From equations (1), (2) and (3) we get
Thus, circumference of the circle with radius cm =26 cm and circumference of second circle,
What will be the circumference of a circle inscribed an equilateral triangle of side 9 cm.
Let be the centre of the inscribed circle of
Since, radius of inscribed circle in a triangle
Now Area of
Semi perimeter of
Radius of inscribed circle cm
Circumference of the circle