Area of circlePresented by h. p. patel Tgt maths
ObjectiveTo find out the area of a circle throughpaper cutting and pasting method.
Pre requisite knowledge• Radius and circumference of the circle.• Equal parts of the circle.• Area of the rectangle.
Materials required• White sheet of paper.• Glazed papers.• Geometry box.• Fevicol/gum.• Scissors.
Procedure Draw a circle with radius r (10 cm). Divide the circle in 16 equal parts. Radius of the circle = r. Circumference of circle = 2πr. Length of green circum. = πr. Length of pink circum. = πr.
Procedure continue - Cut all the sixteen parts of circle with scissor and arrange them as shown in figure. Length of green side = πr. Length of pink side = πr. πr So Length of parallelogram=πr. And breadth = r. r r πr
Observation From above activity we can observe that, if we will make small part of circle and rearrange them like a parallelogram , it become a rectangle with length πr and breadth r. πr So, area of parallelogram(rectangle) = length x breadth r = πr x r r = πr2 πr
ResultArea of a circle with radius r is πr2. Area of circle = πr2 r
Test your knowledge1. Find the area of a circle with radius 7 cm.2. Find the area of a circle, if circumference of the circle is 132 cm.3. Find the radius of a circle, if area of the circle is 154 cm2.