There are two ways to choose the polar angle range in polar coordinate system. The polar angle θ corresponding to point P can be the angle at which the positive semi-axis of the polar axis rotates counterclockwise to the light OP, and the value of θ can be between 0 and 2 π, or the angle between the light OP and the positive semi-axis of the polar axis, and then the positive and negative can be distinguished. The angle above the polar axis is positive, the angle below is negative, and the range of θ is between-π and π. For the circle represented by p=Rcosθ, if it is written as an interval, the value range of θ is -π/2 to π/2, and it can also be written as two intervals of 0 to π/2 and 7π/4 to 2π. A simple verification method is that the polar diameter p must always be non-negative, so the range of θ can also be obtained from p=Rcosθ≥0. View original post >>