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The Circle - Problem 1 11,381 views

Teacher/Instructor Carl Horowitz
Carl Horowitz

University of Michigan
Runs his own tutoring company

Carl taught upper-level math in several schools and currently runs his own tutoring company. He bets that no one can beat his love for intensive outdoor activities!

Given the coordinates of center of a circle (h, k) and the radius (r), plug the values into the general equation of a circle: r^2 = (x-h)^2 + (y-k)^2. Be careful to change the signs accordingly when plugging in the values for h and k.

Finding the equation for a circle with a specified center and radius. So really all we have to do when we're looking for the equation for a circle is look for our general equation.

So our equation is just r² is equal to x minus 8² plus y minus k² where h and k are the coordinates of the center, so really all we have to do is take the information we're given and plug it in.

So our radius is 5, so we go to our r plug in 5, 5² is easy enough to do, we end up with 25 is equal to x minus h, h is the coordinate of our center so we go to our -1, plug that in and we end up with x minus -1, x plus 1 and then add it to do the same thing for the y coordinate of the center plugging in 2 for k and we end with y minus 2 quantity squared.

So really to find the equation of a circle all we have to do is remember the general formula and then plug in all the information.