How do you figure out where a rose curve starts? like how would you figure out where r=-6sin(5x) started on a graph?

A sine graph starts at 0, so the rose curve will also start at zero. A cosine graph starts at the maximum value, so whatever the a value is that is where the rose curve starts. For example if it was a cosine function instead of a sine function then it would start on the left side of the x axis on 6.