Given is the following equation of a circle, for which I've to determine its centre and radius. I'm running into some difficulties when I'm trying to complete the squares.

This leads me to believe the centre would be (1, -2). Now to find its radius I'll just complete the squares and simplify:

This obviously isn't correct, -1 being kind of a weird radius

. So what am I doing wrong here? The correct answer (according to my textbook) should be r=3. I guess I'm missing something with completing the y-part, since -1 + 4 = 3, but can't wrap my head around it...

Any handy tips for solving these kind of exercises?