# Thread: Another complex number question:

1. ## Another complex number question:

"If z=cis(ø), find the argument and modulus of 1-z"

2. Originally Posted by karldiesen
"If z=cis(ø), find the argument and modulus of 1-z"
Let's say that $\phi \ne 0$.

Then because $1-\cos(\phi)>0$ implies $\arg(1-z)=\arctan\left(\frac{\sin(-\phi)}{1-\cos(\phi)}\right)$.

3. Originally Posted by karldiesen
"If z=cis(ø), find the argument and modulus of 1-z"
Do you know what "cis" means? If so you can write z in the form "a+ bi", subtract from 1 and then find the argument and modulus of that.