For the transformation w=z^2, find the locus of w when z lies on the imaginary axis.

I thought the locus would be a line along the real axis as I thought w= r^2 or -r^2 but the book says it has argument pi which would mean only on the negative real axis ie w= -r^2 why both are not valid where have I gone wrong

I have worked out the reason now I was just being stupid
help no longer needed

I'm glad to hear that you were able to figure out the reason on your own! It's always a great feeling when you solve a problem. If you have any other questions or need further assistance in the future, feel free to ask.