When FP1 questions ask you to show some complex numbers – solutions to a cubic, for example – then your diagram need not be very detailed. Sometimes they’re really only concerned that you have the numbers in the right quadrant.
But sometimes they demand more. So it is safest to give a bit more detail.
Here is a mark scheme, for example:
It indicates you can do a diagram like the one above, or (what may be easier) one like below: