# how to solve equations for polynomials coefficients?

I am new to SAGE so sorry if this question is trivial. I have this code

```
R2.<a0,a1,a2,a3, a4,b0,b1,b2,b3, b4,z,w,l,E,E1,v,t> = PolynomialRing(ZZ,17)
R.<x> = PowerSeriesRing(R2)
p = a1*x -a1*z*x**2+ a3*x**3+a4*x**4 +O(x**12)
k = b1*x+b2*x**2+ b3*x**3+b4*x**4 +O(x**12)
p1 = p.derivative()
p2 = p1.derivative()
y =2/x*(z-v*x)-E
x=2/x*a1*w*x**2
g=x*(p2 +y*p-x-E1*k)
v1=g.coefficients()
solve(v1[0],a3)
```

I am getting this error **a3 is not a valid variable.**

My question is how to solve equations for polynomials coefficients?

`solve`

is supposed to have (a listof) symbolic expressions (or symbolic expressions) as first argument, and (al list of) symbolic variables as second argument. in the call`solve(v1[0], a3)`

, both arguments are polynomials :A possible workaround is :

but note that

I do not understand what

is supposed to mean...