1. Finding Circumference and Area of a Circle Brought to you by powerpointpros.com

2. What is Pi?

3. Pi is a key “ingredient” in the “recipe” for finding the circumference and area of circles.

4. The Value of Pi The value of pi is a decimal number that goes on forever. Here are just some of the digits that make up pi: 3.1415926535897932384626433832795028841971693993751058209749445923 0781640628620899862803482534211706798214808651328230664709384460 9550582231725359408128481117450284102701938521105559644622948954 9303819644288109756659334461284756482337867831652712019091456485 6692346034861045432664821339360726024914127372458700660631558817 4881520920962829254091715364367892590360011330530548820466521384 1469519415116094330572703657595919530921861173819326117931051185 4807446237996274956735188575272489122793818301194912983367336244 0656643086021394946395224737190702179860943702770539217176293176 7523846748184676694051320005681271452635608277857713427577896091 7363717872146844090122495343014654958537105079227968925892354201 9956112129021960864034418159813629774771309960518707211349999998 3729780499510597317328160963185950244594553469083026425223082533 4468503526193118817101000313783875288658753320838142061717766914 7303598253490428755468731159562863882353787593751957781857780532 171226806613001927876611195909216420198…

5. Approximation of Pi Because pi is a value that continues infinitely, it is often approximated to be the value of 3.14.

6. The Pi Symbol The symbol for pi is this: π

7. Finding the Circumference of a Circle using Pi

8. The Circumference Formulas There are 2 acceptable circumference formulas. Both produce the same results. Here they are: C=πd C=2πr Variables: C=Circumference D= Diameter R=Radius

9. Using the Circumference Formulas Here are the formulas: C=πd C=2πr When given the diameter of a circle, you should use the first formula, whereas if you’re given the radius, use the second formula. 5 cm You have been given the radius of this circle. Which formula should you use?

10. Using the Circumference Formulas Now, we should plug in our values into this formula: 5 cm Since we know that pi is approximated as 3.14, we can enter that into our formula… C=2πrC=2(3.14)r And since we can see that our radius is 5 cm, we can enter that into the formula as well. C=2(3.14)5 Now, let’s find the circumference!

11. Using the Circumference Formulas 5 cm Using the formula C=2(3.14)5, we can see that the circumference of this circle is 31.4 cm.

12. Using the Circumference Formulas Here are the formulas: C=πd C=2πr Remember, when given the diameter of a circle, you should use the first formula, whereas if you’re given the radius, use the second formula. 18 yards You have been given the diameter of this circle. Which formula should you use?

13. Using the Circumference Formulas Now, we should plug in our values into this formula: Since we know that pi is approximated as 3.14, we can enter that into our formula… C=πdC=(3.14)d And since we can see that our diameter is 18 yards, we can enter that into the formula as well. C=(3.14)18 Now, let’s find the circumference! 18 yards

14. Using the Circumference Formulas Using the formula C=(3.14)18, we can see that the circumference of this circle is 56.52 yards! 18 yards

15. Finding the Area of a Circle using Pi

16. The Area Formula There is only one are formula, and here it is: A=πr² Variables: A=Area R=Radius

17. Using the Area Formula Here is the formula: A=πr² 10 miles

18. Using the Area Formula Now, we should plug in our values into this formula: 10 miles Since we know that pi is approximated as 3.14, we can enter that into our formula… A=(3.14)r²A=πr² And since we know our radius is 10 miles, we can add that, too! A=(3.14)10² Now that we have all the information we need, we can solve the problem!

19. Using the Area Formula Using the formula A=(3.14)10², we can see that the area of this circle is 314 miles! 10 miles

20. But wait! Since we’re dealing with AREA, our answer should be squared! So, our answer is ACTUALLY 314 miles².

21. Using the Area Formula Here is the formula: A=πr² 22 meters Oh, no! There must be a mistake! We’ve been given the diameter of a circle instead of the radius!

22. Using the Area Formula Well, that shouldn’t be a problem! Since we know that radius= ½ diameter, we can still solve the problem. If we do the math and take 22/2, we get our radius of… 11 meters! 22 meters11 meters

23. Using the Area Formula Now, we can plug the values into our formula: 11 meters Since we know that pi is approximated as 3.14, we can enter that into our formula… A=πr² A=(3.14)r² And since we found our radius of 11 meters, we can add that as well! A=(3.14)11² We have all of our needed information! We can solve the problem!

24. Using the Area Formula Using the formula A=(3.14)11², we can see that the area of this circle is 379.94 meters²! 11 meters

25. Practice with Circumference, Area, and Pi

26. Practice: Multiple Choice What is the value for Pi? a)3.14 b)9.27 c)3.45 d)6.35 e)5 f)Pi is a decimal with an infinite number of digits. The value goes on forever.

27. Practice: Multiple Choice What is Pi often approximated as? a)3.14 b)9.27 c)3.45 d)6.35 e)5

28. Practice: Multiple Choice What is the symbol for Pi? a)& b) c)µ d)π e)® f)¿ g)¥

29. Practice: Circumference and Area Find the circumference and area of each circle. 50 feet Circumference= 314 feet Area= 7,850 feet²

30. Practice: Circumference and Area Find the circumference and area of each circle. 10 cm Circumference= 62.8 cm Area= 314 cm²

31. Practice: Circumference and Area Find the circumference and area of each circle. 4 miles Circumference= 12.56 miles Area= 12.56 miles²