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

What is Pi?

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

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: …

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

The Pi Symbol The symbol for pi is this: π

Finding the Circumference of a Circle using Pi

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

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?

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!

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.

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?

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

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

Finding the Area of a Circle using Pi

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

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

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!

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

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

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!

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

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!

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

Practice with Circumference, Area, and Pi

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.

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

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

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

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

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