PURPOSE
Solve multiple equations with NLSOLVE in Excel (equations from an circuit analysis)

Content of the cells A1 until A4:

= -X2 + X1 + X3 
= -1 -X3 + X4
= 50 - 10*X3 - 4*X2
=-65*X1 + 10*X3 + 25*X4

With

=NLSOLVE(A1:A4,X1:X4)

I get the correct values for X1, X2, X3, X4

PROBLEM
The original values in the exercise were not X1:X2 but i1, ia, ib, ic.
When I use these variables, it does’t work and excel seems to consider these variables as cell range. ok, BUT

QUESTION

1. Why X1, X2, X3, X4 are not being confused with cells?
2. how can I use the variables i1, ia, ib, ic?

Thank you for you help