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Lesson 1: Perimeter

# Finding perimeter when a side length is missing

The video is teaching us how to find the perimeter of a shape. To do this, we need to measure the lengths of all the sides and add them together. Sometimes we have to use clues to figure out the length of a side if it isn't labeled. The perimeter is the total distance around the outside of the shape. Created by Lindsay Spears.

## Want to join the conversation?

• how would you get the area and the perimeter of an circle
• perimeter of a circle is called Circumference

To find circumference of a circle, multiply diameter by Pi value (3.14..):

Circumference = Pi * Diameter

or if you know the radius, the formula will be be:

Circumference = Pi * Radius * 2
Because diameter = 2 * radius

To find Area of a circle, multiply Pi by squared radius. Formula looks like this:

Area = Pi * r²
• At and , why didn't she just add the 4s and add 8 to the other numbers?
• could we find the area of a circle?

The radius of a circle is the distance from the center to any point on the circle.

The number pi is the unending decimal 3.14159265358979323... .
For calculations, 3.14 is a good estimate of pi.

Then the area of a circle is pi times the radius times the radius.

Have a blessed, wonderful day!
• is there no other formula to find the perimeter of the missing sides ?
• I really need to know if you can find the area of a CIRCLE.
• Yes, it is possible. (the area of a circle is pi (3.14159) times the radius of the circle squared (squared = the number to the power of two, or the number times itself))

*pi is usually denoted by the Greek letter π, which is used to represent a constant (its value never changes) value of approximately 3.14159.

*To find the radius of a circle, we can either take the diameter of the circle (distance across the circle) and divide it by two.
Or, by taking a measurement from the center of the circle to any point on the boundary (this is the Radius)
Or, by taking the circumference (the distance around the circle) and dividing it by 2π (2 * 3.14159)

For example, if we know the radius of a circle (lets say 15cm) then we can find the area by taking pi * 15 to the power of 2 (15*15) = (3.14159 * 15^2 = 707)
So, a circle with the radius of 15cm has an area of 707cm

• why did you add so weirdly? to