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Finding the Area of a Circle

Finding the Area of a Circle When finding the areas of other shapes, we used our knowledge of shapes we already knew . For example, to find the area of a parallelogram, we turned it into a rectangle. To find the area of a triangle, we used two triangles to make a parallelogram.

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Finding the Area of a Circle

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  1. Finding the Area of a Circle Whenfinding the areas of othershapes, we used our knowledge of shapes we already knew. Forexample, to find the area of a parallelogram, we turned it into a rectangle. To find the area of a triangle, we used two triangles to make a parallelogram. To find the area of L-shapes,we partitioned into rectangles.

  2. Finding the Area of a Circle To find the area of a circle, we can partition and rearrange to make a rectangle. Watch thisvideo

  3. Finding the Area of a Circle The area of a circle can be found using the formula:

  4. A =r2 The Area of a Circle A = πr2 Calculate the area of a circle with a radius of 10 using the formula above. Draw a diagram before working it out. How would you type it into your calculator? Calculate the area of a circle with a radius of 20 using the formula above

  5. A =r2 The Area of a Circle A = πr2 Calculate the area of a circle with a diameter of 10 using the formula above. How is this different to the previous questions?

  6. A =r2 The Area of a Circle A = πr2 Calculate the area of this shape. Show all of your working out on your whiteboard.

  7. The Area of a Circle A = πr2 These shapes are not drawn to scale. Calculate the areas in your books. You must show your working out.

  8. How are the areas of these shapes related? Canyou explain why?

  9. These shapes have the same areas. Write possible measurements on your whiteboards

  10. These shapes have the same areas. If the radius of circle a is x, what is the diameterof circle b? ? x

  11. These shapes have the same areas. If the diameter of circle b is y, what is the radiusof circle a? y ?

  12. A =r2 The Area of a Circle A = πr2 Calculate of this shape. Show all of your working out on your whiteboard.

  13. A =r2 The Area of a Circle A = πr2 Calculate of this shape. Show all of your working out on your whiteboard.

  14. On your whiteboards:

  15. Title: The area of a circle Find the areas of these shapes in your books. You must show working out.

  16. Title: The area of a circle How is area a related to area b? Why?

  17. Title: The area of a circle How is area b related to area c? Why?

  18. Title: The area of a circle Can you find some others that are related?

  19. Title: The area of a circle A = πr2

  20. Title: The area of a circle A = πr2

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