It we measure the circumference and diameter of various circles, we will find that the ratio of the circumference and their corresponding diameters is always constant. This constant ratio is denoted by the 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 circumferences is 8cm. Find the two circumferences.
Let be the radius of one circle.
The radius of the other circle is cm
Now, the circumference of the circle with radius cm cm --- (1)
and, the circumference of the circle with radius cm --- (2)
The difference of the two circumferences = 8 cm --- (3)
From equations (1), (2) and (3) we get
Thus, the circumference of the circle with radius cm =26 cm and the circumference of the second circle,
Find the circumference of a circle inscribed in an equilateral triangle of side 9 cm.
Let be the centre of the inscribed circle of
Since the radius of the inscribed circle in a triangle
Now the area of
Semi perimeter of
Radius of inscribed circle cm
Circumference of the circle