Consider the code defining two constants:

a=Cos[t]
b=Sin[t]

Suppose that we have another value in terms of Cos[t] and Sin[t], for example,

c=2*Cos[t]+Sin[t]^2

How to show the result of c in terms of a and b, that is, instead of the line above I'd like my computations being showed as

c=2*a+b^2

In other words, how to ask Mathematica to recognize Cos[t] as a?