Circles Javier Soto (click to continue)

Diameter The DIAMETER of a circle is the measurement from one side of the circle, to the opposite edge. It is usually represented by a line that runs through the CENTER of the circle. This LINE is the DIAMETER.

Radius The RADIUS of a circle is like the diameter, but it measures only from the CENTER of the circle to the edge. The radius is always HALF the distance of the diameter. This LINE is the RADIUS.

𝜋 𝜋 𝜋 𝟑 𝝅 Pi (𝝅) 3 x 3.14 Because 𝜋 is 3.14 For example when you see this symbol, just know that it really just means 3.14 This symbol is used a lot when dealing with circles. For example 𝟑 𝝅 Because 𝜋 is 3.14 3 x 3.14 Means 𝜋 WILL ALWAYS BE 3.14

Circumference: circles have perimeters too! There is a special word for getting the “perimeter” of a circle. It’s called Just like “perimeter” for other shapes, CIRCUMFERENCE is the measurement of the distance AROUND the circle. CIRCUMFERENCE.

Circumference: Formula 8cm CIRCUMFERENCE has it’s own special formula: For example, if the DIAMETER of this circle is 8 centimeters, 𝐶=𝑑𝜋 This is telling us that we should MULTIPLY the DIAMETER of the circle times 𝝅, and we know that 𝝅 is ALWAYS going to be 3.14 then the is 25.12, because when we plug in 8 into the “d” and 3.14 into “𝝅“, that’s the answer we get. CIRCUMFERENCE And that’s the answer! :D 𝑪=𝒅𝝅 4 x 3.14 = 25.12

Area of a circle: The GED will also ask you to find the AREA of a circle. The AREA measures what’s INSIDE the circle. The RADIUS is also really important for finding the AREA, so just keep it in mind.

4cm 𝑨=𝜋 𝑟 2 𝑨=𝜋 𝑟 2 Area: Formula 4 4 3.14 x x 50.24 This is the formula AREA for the of a circle: For example, if the RADIUS of this circle is 4 centimeters, 𝑨=𝜋 𝑟 2 This formula tells us that we must multiply the RADIUS of the circle times itself first, then multiple that answer times rcle times𝝅, and we know that 𝝅 is ALWAYS going to be 3.14 then the AREA is 50.24, because when we plug in 4 into the “r”, multiply it by itself (4x4), and then 3.14 into “𝝅“, that’s the answer we get. 𝑨=𝜋 𝑟 2 3.14 x 4 x 4 = 50.24

CHECKLIST! I know what the DIAMETER of a circle is. Make sure you learned the following concepts from this lesson. If you didn’t give the slide another look. If you did, take the quiz below! Don’t know? Refresh your memory I know what the DIAMETER of a circle is. Slide 2 I know what the RADIUS of a circle is. Slide 3 I know what Pi 𝜋 is. Slide 4 I know how to get the CIRCUMFERENCE of a circle. Slide 5 I know how to get the AREA of a circle. Slide 7