The outward rotation of a circle can be described as a helix, which can be expressed in polar coordinates. In polar coordinates, the mathematical model of helix can be described by polar coordinates equation. A commonly used spiral equation is the polar coordinate equation $r = a\cdot\theta$ where $r$ is the radius, $\theta$ is the angle and $a$ is a constant. This equation shows that the radius of the helix increases linearly with the increase of angle. When $ a & gt0$, the spiral rotates outward; When $a