This is one of my exercise problem regarding the limit lesson.

The problem: In the theory of relativity, the mass of a particle with velocity v is

where

is the mass of the particle at rest and c is the speed of light. What happen as

?

I am thinking that the problem is asking me to find the limit of the equation above as v approaches c from the left, but I cannot get rid of the radical sign. I try to rationalize the denominator, but it does not lead me to an answer which I think is correct.

ANY HINT IS APPRECIATED.

Thanks