Which function do I need to rearrange a symbolic expression?

I have an expression of the form:

4t(a+b-c)^2 + (x-a)^2 + (y-b)^2 + (z-c)^2

I need to rearrange it to the form:

(something_without_c) + (c - something_without_c)^2

(And later to something like:

(a - something_without_a_or_b_or_c)^2 + (b - something_without_b_or_c)^2 + (c - something_without_c)^2 ) + something_without_a_or_b_or_c)

This is clearly achievable manually, but coefficients are cumbersome, so I am looking for some machine aid.

Any suggestions?

Answer 1

[Walter Roberson]

You might be able to take advantage of isolate or coeffs