# Solving symbolically equation system

I have an equation system:

*U(t) = R * I(t) + L * I'(t) + uC(t)*

*I(t) = C * uC'(t)*

I want to know value of *I'(t)* and *uC'(t)*, which is *(-I(t) * R + U - uC(t))/L* and *I(t)/C* respectively.

In sage I represent it this way:

```
R = 6; C = 10^(-4); L = 0.1
t = var('t')
U = function('U', t).function(t); I = function('I', t).function(t); uC = function('uC', t).function(t)
equations = [
U == R * I + L * I.diff(t) + uC,
I == C * uC.diff(t)
]
```

but

```
solve(equations, I.diff(t), uC.diff(t))
```

does't seem to be working. (*TypeError: 'sage.symbolic.expression.Expression' object is not iterable*)

why? how can I do this?