Circles

Radius : The radius is a line segment with one end point at the centre and the other end on the circle. It is denoted by ‘r’. r O A Diameter : Diameter is a chord passing through the centre of the circle. It is denoted by ‘d’. O A B d

Relationship between diameter and radius: Diameter of a circle is twice of its radius. Formula: Diameter = 2 x radius Radius = r O r A B d

Pi (π) The ratio of circumference to diameter is constant for all circles. This ratio is called Pi and is written as π. Where π = C = π ⇒ C = πd ⇒ C = 2πr d 22 7

Example 1 : Find out the Diameter of a circle whose radius is 5 m. Solution Given:- radius(r)= 5 To Find:- diameter(d) Diameter of a circle (d) = 2 x radius = 2 x 5 = 10m (ans) Example 2 : Find out the radius of a circle whose diameter is 8 m. Solution Given:- diameter(d) = 8 To Find:- radius(r)

Solution Given:- radius(r)= 21 To Find:- circumference(c) Example 3 : Find out the circumference of a circle whose radius is 21 m. Solution Given:- radius(r)= 21 To Find:- circumference(c) Circumference (C) = 2πr 3 Divide 21 and 7 by 7 = 2 x 22 x 3 = 132 m (ans) Example 4 : Find out the radius of a circle whose circumference is 44m. Solution Given:- circumference(c) = 44 To Find:- radius(r) Circumference (C) = 2πr = 7 m (ans) Divide 44 and 44 by 44

Solution Given:- circumference(c) = 44 To Find:- diameter(d) Example 5: Find out the circumference of a circle whose diameter is 21 cm. Solution Given:- diameter(d) = 21 To Find:- circumference(c) Circumference (C) = πd 3 Divide 21 and 7 by 7 C = 22 x 3 = 66 cm (ans) Example 6: Find out the diameter of a circle whose circumference is 44cm. Solution Given:- circumference(c) = 44 To Find:- diameter(d) Circumference (C) = πd 2 Divide 44 and 22 by 22 d = 2 x 7 = 14 cm (ans)

Try these Find out the circumference of a circle whose diameter is 63 cm. Find out the radius of a circle whose circumference is 66 m.