How can z = a * cost + IB * Sint (a, B are real constants) be expressed as a rectangular coordinate equation? By the way, let me talk about the relationship between complex equation and rectangular equation

How can z = a * cost + IB * Sint (a, B are real constants) be expressed as a rectangular coordinate equation? By the way, let me talk about the relationship between complex equation and rectangular equation

In contrast, the complex equation of x = acost, y = bsint is introduced to calculate the complex number, which has no real significance