The law of cosines relates the pole-to-point distance r, the pole-to-center distance d, and the fixed center-to-point radius R. Because the angle between the pole-to-center direction and the point direction is θ - φ, the cosine term becomes cos(θ - φ). Rearranging that geometric relationship gives the stated quadratic equation in r.
The parameter d specifies how far the circle’s center lies from the pole, while φ specifies the direction from the pole to that center. Together, they locate the circle relative to the polar reference system. The parameter R still determines the circle’s size, so the equation separates position, orientation, and radius.
The difference θ - φ measures the angular separation between a point and the direction of the circle’s center. Consequently, the equation responds to the point’s direction relative to that center rather than to an unrelated fixed angle. This makes the angular structure useful when examining orientation and symmetry in polar graphs.
Graphing begins by identifying whether the circle is centered at the pole or displaced from it. For a pole-centered circle, every plotted point has the same radial value R. For an offset circle, the quadratic relation determines allowable r values for selected angles, allowing the resulting points to be plotted in polar coordinates.
At an intersection, the same polar point must satisfy both circle equations, so the equations can be considered together to identify common radial and angular values. This approach connects the algebraic conditions with the geometric locations where the curves meet, supporting intersection analysis in analytic geometry and polar-coordinate work.
They express circular geometry directly through radial distance and angle, which makes them suitable for problems already organized around polar coordinates. In calculus, the equations provide a circular curve in a polar form; in modeling, they represent locations relative to a pole while retaining clear information about the circle’s center and radius.