Basic Technical Mathematics, 11th Edition

21.3 The Circle

• Standard Equation • Symmetry • General Equation • Calculator Graph

We have found that we can obtain a general equation that represents a straight line by considering a fixed point on the line and then a general point P(x, y) that can represent any other point on the same line. Mathematically, we can state this as “the line is the locus of a point P(x, y) that moves from a fixed point with constant slope along the line.” That is, the point P(x, y) can be considered as a variable point that moves along the line.

In this way, we can define a number of important curves. A circle is defined as the locus of a point P(x, y) that moves so that it is always equidistant from a fixed point. We call this fixed distance the radius, and ...