Question 1170558
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You are given a complex number in cis-form  

    z = {{{9*cis(3pi/2)}}}.


It means that the modulus of this complex number is 9, while its argument is {{{3pi/2}}}.


The angle  {{{3pi/2}}}  corresponds to the negative direction of the y-axis.


So, in the plane (x,y) you go 9 units down along y-axis and mark there your point 
by the pen on the graph paper.  That is all: the sketch is ready.


The a + bi form is  a + bi = 0 + (-9)i , meaning 9 units down on y-axis.
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Solved, with all necessary explanations.