1. The problem statement, all variables and given/known data Find the modulus and argument of z=1-cos(a)-i*sin(a) 2. Relevant equations mod(z)=sqrt(a^2+b^2) 3. The attempt at a solution mod(z)=sqrt((1-cos(a))^2+(-sin(a))^2) =sqrt(2-2cos(a)) arg(z)=arctan((-sin(a))/(1-cos(a))) This is as far as I can get, I have asked my math teacher but he is not very familiar with thise. my textbook gives mod(z) as 2sin(2a) and arg(z) as (a-pi)2 BTW this question is from the IB math textbook, there exists a solutions manual but I do not have it... the question is 11.2, 19 a) Thanks in advance!