Hey I know this is really simple and silly, I used to find this really easy, I've been confused by a book and now feel rather stupid at not being able to even rearrange equations.. I get it right, right, right and then suddenly I get one written exactly upside down when compared to the book's answer.

Here's an upside down one:

$\displaystyle F_{el} = \frac{1}{4\pi\epsilon_{0}} \frac{q1q2}{r^2}$ to make $\displaystyle r$ the subject

I did

$\displaystyle 4\pi\epsilon_{0} F_{el} = \frac{q1q2}{r^2}$

then

$\displaystyle \frac{4\pi\epsilon_{0}F_{el}}{q1q2} = r^2$

then

$\displaystyle \sqrt\frac{4\pi\epsilon_{0}F_{el}}{q1q2} = r$ or $\displaystyle r=\pm\sqrt\frac{4\pi\epsilon_{0}F_{el}}{q1q2}$

Their answer was

$\displaystyle r=\pm\sqrt\frac{q1q2}{4\pi\epsilon_{0}F_{el}}$

I've spent a few hours rereading my chapters and getting a bit upset...what have I done wrong?