In mathematics, "r, θ" refers to the polar coordinate system, which represents points in a two-dimensional space using a radius and an angle. Here, "r" denotes the distance from the origin (the center point), while "θ" (theta) indicates the angle measured from the positive x-axis. This system is particularly useful for describing circular and spiral shapes. Polar coordinates can be converted to Cartesian coordinates (x, y) using the formulas: x = r \cdot \cos(θ) and y = r \cdot \sin(θ) . This conversion allows for easier calculations in various applications, including physics and engineering, where circular motion is involved.