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Grade 7:  The Learning Equation Math

31.02 Circle Problems

3icon.gif (4368 bytes)

Measurement

Refresher pp 56-57

Learning Outcomes:

The student will:

Circumference

circle2.gif (1873 bytes)

r = radius

d = diameter

C = Circumference

p = C/d = 3.14...

source:  Circle Notes

Area

circle_area1.gif (2748 bytes)

C = 2pr

C/2 = pr

The circle (C = 2pr) shown has the area shaded blue and red. Consider the sectors as pieces joined on the circumference, able to be opened out in the two halves. By inter-weaving the sectors, we get the picture shown below where:
  • the base of the parallelogram is half of the circumference (pr)
  • and the height is the radius (r)

base(b)

parallelogram

A = bh

circle_area.gif (3586 bytes)

height(h) = r

 

A = bh = pr(r) =  pr2

Source:  Lesson Plan - Area of a circle

 

Drag the handle to change the size of the radius and diameter. Study the change in circumference and area as you do so.

 

Circle Calulator

  • Enter a value in for one of the following
  • Click the Enter

p = C/d = 3.14...

Radius(r): cm
Diameter(d): cm
Circumference(C): cm
Area(A): cm2

 

Key Terms: A-E F-J K-O P-R S-Z

diameter, radius, circumference, area, dimensions, perimeter, trapezoid, mass, volume

Prerequisite Skills:

Circle Measurement:  Grade 7 Lesson 31.01

 

 

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Comments to:  Jim Reed
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