complex algebraic function simplify

[Gribouillis]

Use an expression that must be zero in solve() as the docstrings says

>>> import sympy
>>> a, C, t, E, R1, R2, i = sympy.symbols("a, C, t, E, R1, R2, i")
>>> a
a
>>> C
C
>>> z = i - E/(R1 + 1/(R2 + a * i * t / (C-i)))                                              
>>> sympy.solve(z, t)                                                                        
[(C - i)*(-E*R2 + R1*R2*i + i)/(a*i*(E - R1*i))]