Is e=mck Compatible with Einstein's Theory of Relativity?

[GautamAishwarya]

when theory of relativity declares speed of light to be the limit for speeds of all matter and energy and information. then, how can einstein in his mass-energy eqn talk about c squared. we can't talk about any velocity more than c.
it is possible that e = mck where the value of constant k shall be equal to value(only of magnitude only) of c.
also ,
h.nu is directly proportional to mc, and ratio of h.nu to mc is the constant with value equalling c.

 

[HallsofIvy]

Don't confuse arithmetic with physics. c is a number (with units). It happens to be the speed of light but it is just a number. c² is another number that is NOT the speed of light. In fact, since c² has units of length²/time², it cannot be the speed of anything. If you want to say "the value of constant k shall be equal to value(only of magnitude only) of c", fine (well, not "magnitude only" because you have to take the units into account), but that was what was meant all along.