Hi, my name is Charles, I am one of the math teachers from the Maxim workshop. I am just telling now how to do some math. I am going to show you how to find the diameter of a circle. Now the first thing you need to know about a circle is some of its properties. So the origin of the circle lies at the center, and that's what we use to define the diameter and the radius. Now you have any point from the circle starting from here and going to the origin, say, is equal to our radius. Now, if you have twice that length, so extending from this point through the origin and then touching the other side, you have the diameter. So put this as radius and this I have labeled 'd' as diameter and 'r' as radius. Again you have another property which is the actual perimeter of the circle and that leads to the circumference. So I'll put 'c' all the way round and we're done. So, now in order to find the diameter of the circle which is the distance leading through the circle from one side to the other, and through the origin, we are going to need to establish a measurement of our radius. So we know that the radius times two provides diameter, so 2r equals d. So imagine if we had a circle that measured 3 centimeters for its radius, that would imply that we would need to use this equation to calculate the diameter. So we say 2 times 3cm equals 6 centimeters. And remember, we use the units of centimeters because our radius is in centimeters. So this equals our diameter. Now, we are going to look at our circumference. So C equals circumference. So, a circumference is again the perimeter of the circle so the equation we have for the circumference is that c equals pi d. Okay, so the pi, we know that this equals 3.142, but what we are going to do for the ease of this calculation is we are going to take it down to 3 so pi is approximately equal to 3 for this calculation. Now, if we want to find d, we are going to need to bring this pi to the other side, so there is a bit of fitting around we need to do first and that's pretty much say, we have pi multiplying by d, when we take it to the other side across the equals sign, we are going to be dividing by c. So c divided by pi and that equals d. So c equals 18. The next question might be what is the diameter equal to. Now in order to find out, we are going to need to use this equation here. So we plop in our value for c and we need a value for pi, we have defined that here as being approximately equal to 3. So below, we've got 18 divided by three. Now 18 divided by 3 again is 6 centimeters. So that's our solution for d where we have a circle with a circumference of 18 centimeters and we approximate the number 3 equals pi and that's basically how to calculate the diameter of a circle.

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