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You now know how to write the equation of a circle in standard form (x - h)2 + (y - k)2 = r2 as an equation of the form Ax2 + Ay2 + Cx + Dy + F = 0.

Now you'll learn how to rewrite the equations of a circle from the form Ax2 + Ay2 + Cx + Dy + F = 0 to the standard form.

Why should you know about two forms of an equation?

Good question. In standard form it is easy to tell what the centre and radius of the circle is, but in general form this is quite difficult.

In order to graph a circle given an equation in general form, we must first transform the equation into standard form. This is not always easy and requires a method called Completing the Square.

After reviewing the completing the square method, follow through some examples below for some practice.