$\displaystyle m = \frac{1}{\sqrt{1-k^2}}$

I need to solve for k. Is this the correct steps?

$\displaystyle \sqrt{1-k^2}m = 1$

$\displaystyle \sqrt{1-k^2} = \frac{1}{m}$

$\displaystyle \pm(1-k^2) = \frac{1}{m^2}$

But I get stuck here. How would I isolate for k?