# POLQ 3 | Lesson 4 | Explore (Equation of a Circle)

Equation of a circle.

The general form for the equation of a circle is $$ax^2 + by^2 + cx + dy + e = 0$$, and the circle-radius form of the circle equation is $$(x–h)^2 + (y–k)^2 = r^2$$ , with the center being at the point $$(h, k)$$ and the radius being “$$r$$”.

Think about the following question. The endpoints of the diameter of a circle are $$(-4, 0)$$ and $$(4, 0)$$. What are the coordinates of the center of this circle?