## anonymous one year ago MEDAL AND FAN 1 All circles are similar to each other. True False 2 Find the exact area of a circle having the given circumference. 8 A = 4√2 16 64 3 Find the exact area of a circle having the given circumference. 3 A = 2.25 3 9 4 Find the exact circumference of a circle with an area equal to 36 sq. in. 12 18 324

1. mathstudent55

1. T

2. mathstudent55

2. Use the circumference formula to find the radius. Then use the area formula to find the area.

3. mathstudent55

3. Solve it same way as 2.

4. mathstudent55

4. Use the area formula to find the radius. Then use the circumference formula to find the circumference.

5. mathstudent55

If you have questions, just ask.

6. anonymous

cant remember the area formula for a circle

7. anonymous

can you work out number 2 for me?

8. anonymous

@mathstudent55

9. mathstudent55

Here are the formulas you need. $$\Large C_{circle} = 2 \pi r$$ $$\Large A_{circle} = \pi r^2$$

10. anonymous

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11. mathstudent55

2 Find the exact area of a circle having the given circumference. 8 A = 4√2 16 64 If the circumference is 8, we set 8 equal to teh circumference formula and find the radius. $$\large C_{circle} = 2 \pi r$$ $$\large 8 = 2 \pi r$$ $$\large \dfrac{8}{2 \pi} = \dfrac{2 \pi r}{2 \pi}$$ $$\large \dfrac{4}{\pi} = r$$

12. mathstudent55

You stared it out correct. You need to divide both sides by pi. |dw:1438148608264:dw|

13. mathstudent55

14. anonymous

do i need to divide 4 by pi or is that the final radius?

15. mathstudent55

No. Don't divide. The problem wants an exact area, so we can't divide by pi and give an approximate decimal. We need to keep pi in the radius. Now we find the area.

16. mathstudent55

$$\large A = \pi r^2$$ $$\large A = \pi \times \left( \dfrac{4}{\pi} \right) ^2$$ Ok so far with the area?

17. mathstudent55

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18. mathstudent55

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19. anonymous

so the answer is $16$

20. anonymous

16 pi

21. anonymous

thanks

22. mathstudent55

No. Not 16*pi It's 16/pi

23. mathstudent55

Wait. There is no pi at all in problem 2 or in the choices. Was the circumference 8 or 8pi?