Question 831787
You are asking a hypothetical question and could just as well be asking a realistic application question.  You would obtain a formula FOR c instead of just a formula WITH c.  As written, what would YOUR formula mean?  Would you want to find the value for c, but you have it embedded in an expression in a formula which looks different?


Imagine a real situation in which you know the values for x, y, z, r, and a, but you need to know and make practical use of the value for c.  You solve the equation which contains c for the variable c; and so you will then have a way to compute c.