To figure out the length of that line, so this is the radius, we could figure out a change in x. So how can we figure that out? Well, we can set up a right triangle and essentially use the distance formula which comes from the Pythagorean Theorem. That line right over there, that is going to be the radius. So, for example, for example, this distance. To be the distance between the center and any point on the circle. And now, let's think about what the radius of the circle is. So, the x-coordinate is negative one and then the y-coordinate is one. And the center of theĬircle is just going to be the coordinates of that point. Alright, let's work through this together. I want you to pause the video and see if you can figure out Is a point that happens to sit on the circle. I guess, maroonish-red point right over here is theĬenter of the circle, and then this blue point

So we have a circle here and they specified some points for us. If you imagine the two points had a horizontal and vertical line connecting them, this would make a right triangle. Now, how do you find the distance between two points.

Well, the radius is the distance from the center of the circle to the edge, and the other point we know is by defiition on the edge. In fact you only know for sure of one point since it tells you. There are no points directly above, below or to the left or right of the center you can gauge the radius from. Thankfully it tells us the center, so we can handle the first half of the equation. Now the video starts giving a circle, where we know one point on the circle. Some super simple ones are adding 2 to the x or y coordinate. This means if you went a distance of 2 away from that center point you would be on the circle. so for instance (x-2)^2 + (y-3)^2 = 4 would have the center at (2,3) and have a radius of 2 since 4 = 2^2.

First you need to know that the equation for a circle is (x-a)^2 + (y-b)^2 = r^2 where the center is at point (a,b) and the radius is r.

Circle geometry equations