In the theory of relativity, the mass of a particle with velocity v is
where is the rest mass of the particle and c is the speed of light in vacuum. Find the inverse function of f.
I've tried to make v the subject and I got this,
When I square root both sides to get v, should I choose the +ve or the -ve square root?
The v here is just the speed and no direction is involved here, am I right?