Graph a Circle from its Standard Equation

This video introduces the idea of graphing a circle from the standard equation. The standard equation of a circle with radius r and center (h, k) is (x - h)^2 + (y - k)^2 = r^2.

The general strategy for graphing a circle is to first find the radius and the center of the circle. Then, plot the center and use the radius to find the points directly above or below the center (vertically) and to find the points to the left and right of the center (horizontally).

For determining the x value of the center, think about which x value would make the expression involving x equal to zero. The y value of the center can be found in a similar manner focusing on the expression involving y. The equation is equal to the radius squared, so taking the square root of the numerical side of the equation can find the radius of the circle.

Khan Academy exercise to practice: