1. Circle Formulae 2
The area
of a circle
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2. Click the mouse only when you see or
If you click too soon you will miss the best bits.
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Click to see
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3. The area
of a circle
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4. Circumference =  × Diameter Now, what about the area?
We saw in Circle Formulae 1 that…
Circumference
=  × Diameter
Now, what about the area?
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5. Click to see the circle open
Imagine a circle made out of strands of beads.
Open it out.
Click to see the circle open
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6. Click to see the circle open again
Let’s watch that again.
Click to see the circle open again
radius (half the diameter)
circumference
It’s a triangle!
base = circumference
height = radius (half the diameter)
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7. circle Area of the triangle
We know how to find the area of a triangle.
radius (half the diameter)
circumference
circle Area of the triangle
Area of the triangle
= Base × Height 2
= Circumference × Radius 2
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8. Summary
= Circumference × Radius 2
Area
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9. Area of circle

10. EXERCISE
Calculate the area of a circle with diameter 9 cm
Calculate the exact area of circles with the radius below:
a. 2.8 cm c. 35 cm
b. 12 cm d. 50 cm
3. Calculate the area of the shaded region as shown in the figure below:

11. Determine the circumference of the shaded parts in the figure below

12. The End
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