SOLUTION: Find polar representation of z= cosa-i.sina ,a€[0,2π).

In short terms, using polar presentation form  z = (r,),


    z = (1,-a),


where the first argument in the parentheses is the modulus, equal to 1, while the second argument is the polar angle, equal to "-a".


Or, if you want to have the argument "-a" between 0 and , you may use 


    z = (1,).


It is THE SAME point in a polar coordinate plane.