Area of Circle

Center of circle	Radius of circle	Diameter of circle	Chords of circle	Semi-circle
Circumference of circle	Interior of circle	Exterior of circle	Sector of a Circle	Segment of a Circle
Area of Circle	Arc of Circle	Properties of Circle	Difference Between Circle & Semi Circle

Before you study this concept, you are advised to read: What is Circle ? Formula for Area of Circle = π radius2 Find area of circle when radius is given Example 1: Find area of circle, if radius is 7 cm Solution: As given in the question: Radius = 7 cm Apply formula of Area of Circle: Area of Circle = π r 2 Put the value of radius & π and we get: = (22/7) X 7 2 Expand the above exponential form and we get: = 22/7 X 7 X 7 Solve the expression and we get: = 154 Hence, Area of Circle = 154 cm2 Find area of circle when diameter is given Example 2: Find area of circle, if diameter is 14 cm Solution: As given in the question: Diameter = 14 cm This question is solved in two part: Part 1 : Find Radius of Circle Part 2 : Find Area of Circle Part 1 : Steps to find Radius of Circle : Apply formula to calculate Radius of Circle: Radius = diameter/2 Put the value of diameter and we get: Radius = 14/2 Solve the division expression and we get: = 7 Therefore, Radius = 7 cm Part 2 : Steps to find Area of Circle : Apply formula of Area of Circle: Area of Circle = π r 2 Put the value of radius (calculated in Part 1) & π and we get: = 22/7 X 72 Expand the above exponential form and we get: = 22/7 X 7 X 7 Solve the expression and we get: = 154 Hence, Area of Circle = 154 cm2 Find radius of circle when its area is given Example 3: Area of circle is 314 cm2, find its radius.( value of π = 3.14) Solution: As given in the question: Area of circle = 314 cm2 Apply the formula of Area of Circle: Area of Circle = π r 2 Put the value of area of circle & π and we get: 314 = 3.14 r2 Divide both sides by 3.14 and we get: 100 = r2 Take square-root on both sides and we get: 10 = r Or we can write it as: R = 10 Hence, radius of circle is 10 cm Find diameter of circle when its area is given Example 4: Area of circle is 78.5 cm2, find its diameter.(use value of π = 3.14) Solution: As given in the question: Area of circle = 78.5 cm2 This question is solved in two part: Part 1 : Find Radius of Circle Part 2 : Find Diameter of Circle Part 1 : Steps to find Radius of circle : Apply the formula of Area of Circle: Area of Circle = π r 2 Put the value of π and area of circle and we get: 78.5 = 3.14 r 2 Divide both sides by 3.14 and we get: 25 = r 2 Take square-root on both sides and we get: 5 = r Or we can write it as: R = 5 Therefore, radius of circle is 5 cm Part 2 : Steps to find diameter of circle : Apply formula to calculate Diameter: Diameter = 2 X Radius Put value of radius (calculated in Part 1) and we get: Diameter = 2 X 5 Solve the above multiplication expression and we get: = 10 Hence, diameter of circle is 10 cm Find area of circle when circumference is given Example 5: Circumference of circle is 22 cm. Find Area of circle. Solution: As given in the question: Circumference of circle = 44cm This question is solved in two part: Part 1 : Find Radius of Circle Part 2 : Find Area of Circle Part 1 : Steps to find Radius of Circle : Apply formula to calculate Circumference: Circumference = 2 π r Put the value of circumference & π and we get: 22 = 2 (22/7) (r) Divide both side by 2 and we get 11 = (22/7) (r) Multiply both sides with 7/22 and we get: 7/2 = r Convert the fraction into decimal and we get = 3.5 Therefore, radius of circle = 3.5 cm Part 2 : Steps to find Area of Circle : Apply formula of Area of Circle: Area of Circle = π r 2 Put value of radius (as calculated in Part 1) & π ( as 3.14) and we get: Area of Circle = 3.14 X 3.52 Expand the above exponential form and we get: = 3.14 X 3.5 X 3.5 Solve the above multiplication process and we get: = 38.5 Area of Circle= 38.5 cm2