Originally Posted by a-j

Good point.
The problem is going from sqrt(1/-1) to sqrt(1)/sqrt(-1)
1/i = -i, so in fact it should start out

5) sqrt(-1/1)=sqrt(1/-1)
6) sqrt(-1)/sqrt(1)=-sqrt(1)/sqrt(-1)
7) sqrt(-1)*sqrt(-1)=-sqrt(1)*sqrt(1)
8) sqrt(-1)^2=-sqrt(1)^2
9) -1=-1

The square root properties (sqrt(a/b) = sqrt(a)/sqrt(b)) don't exactly work the same for complex numbers.