Learn the Class 9 Madhyamik Mathematics Circumference and Area of Circle Formulas with easy explanations, KaTeX formulas, and solved examples. This page covers the circumference and area of a circle, semicircle, quadrant, and circular ring (annulus) for quick revision and exam preparation.
Chapter 16 and 18 – Circumference and Area of Circle | Class 9 Flash Formula
Circumference and area of a Circle
Let 'r' be the radius of the circle
(i) Circumference = 2πr
(ii) Area = πr²
Example :
Radius = 7 cm
Circumference = 2 × π × 7
= 14π
= 14 × 22/7
= 44 cm
Area = π × 7²
= π × 49
= 22/7 × 49
= 154 cm²
Circumference and Area of a Semi-circle
Let 'r' be the radius of the circle
(i) Circumference = πr + 2r
(ii) Area = 1\over 2πr²
Example :
Radius = 7 cm
Circumference = π × 7 + 2 × 7
= 22 + 14
= 36 cm
Area = π × 7^2\over 2
= 154\over 2
= 77 cm²
Circumference and Area Quadrant of a Circle
Let 'r' be the radius of the circle
(i) Circumference = 2r + 1\over 2 × πr
(ii) Area = 1\over 4×πr²
Example :
Radius = 14 cm
Circumference = 2 × 14 + π × 14\over2
= 28 + 22
= 50 cm
Area = 1\over 4 × (π × 14²)
= 1\over 4 × 22\over 7 × 196
=1\over 4 × 616
= 154 cm²
Area of Circular Ring
Let R and r be the radii of the external and internal circles, then
Area = π(R² − r²)
Example :
Outer Radius (R) = 10 cm
Inner Radius (r) = 7 cm
Area = π(10² − 7²)
= π(100 − 49)
= 51π
= 160.29 cm²
You have reached the end.