How can I eliminate "rootof", when I use vpasolve for equations

Hello,

I tried to solve an equation, but I could not reach the equation of solutions even I use vpasolve? What do you think problem is? Also, I use Matlab 2015(a).

Code is given below:

syms  x p  a  b  w k m pp aa B t g ww kk A AA f 
x2= ((B*ww - b*w + A*(k - 1))*(a^2*aa + aa^3*k - aa^3 - 4*B*a*m + 4*aa*b*m - a^2*aa*k))/(- 16*B^2*m^2 - 16*B*a*aa*k*m + 16*B*a*aa*m + a^4*k^2 - 2*a^4*k + a^4 - 2*a^2*aa^2*k^2 + 4*a^2*aa^2*k - 2*a^2*aa^2 + 8*a^2*b*k*m - 8*a^2*b*m + aa^4*k^2 - 2*aa^4*k + aa^4 + 8*aa^2*b*k*m - 8*aa^2*b*m + 16*b^2*m^2) - ((B*w - b*ww + AA*(k - 1))*(a*aa^2 + a^3*k - a^3 - 4*B*aa*m + 4*a*b*m - a*aa^2*k))/(- 16*B^2*m^2 - 16*B*a*aa*k*m + 16*B*a*aa*m + a^4*k^2 - 2*a^4*k + a^4 - 2*a^2*aa^2*k^2 + 4*a^2*aa^2*k - 2*a^2*aa^2 + 8*a^2*b*k*m - 8*a^2*b*m + aa^4*k^2 - 2*aa^4*k + aa^4 + 8*aa^2*b*k*m - 8*aa^2*b*m + 16*b^2*m^2) - (2*(a*w - aa*ww)*(B*a^2 + B*aa^2 - 2*a*aa*b - B*a^2*k - B*aa^2*k + 2*a*aa*b*k))/(- 16*B^2*m^2 - 16*B*a*aa*k*m + 16*B*a*aa*m + a^4*k^2 - 2*a^4*k + a^4 - 2*a^2*aa^2*k^2 + 4*a^2*aa^2*k - 2*a^2*aa^2 + 8*a^2*b*k*m - 8*a^2*b*m + aa^4*k^2 - 2*aa^4*k + aa^4 + 8*aa^2*b*k*m - 8*aa^2*b*m + 16*b^2*m^2) - (2*(aa*w - a*ww)*(4*B^2*m + a^2*b + aa^2*b - 4*b^2*m - 2*B*a*aa - a^2*b*k - aa^2*b*k + 2*B*a*aa*k))/(- 16*B^2*m^2 - 16*B*a*aa*k*m + 16*B*a*aa*m + a^4*k^2 - 2*a^4*k + a^4 - 2*a^2*aa^2*k^2 + 4*a^2*aa^2*k - 2*a^2*aa^2 + 8*a^2*b*k*m - 8*a^2*b*m + aa^4*k^2 - 2*aa^4*k + aa^4 + 8*aa^2*b*k*m - 8*aa^2*b*m + 16*b^2*m^2)
 simplify(vpasolve(x2,aa))

and my result is :

 RootOf(B*k*ww*z^3 + 2*A*k*z^3 - b*k*w*z^3 + b*w*z^3 - B*ww*z^3 - A*k^2*z^3 - A*z^3 + B*a*k*w*z^2 - a*b*k*ww*z^2 + a*b*ww*z^2 + 2*AA*a*k*z^2 - AA*a*k^2*z^2 - B*a*w*z^2 - AA*a*z^2 + a^2*b*k*w*z - 4*A*b*k*m*z - 4*AA*B*k*m*z + 4*A*b*m*z + 4*AA*B*m*z - B*a^2*k*ww*z + A*a^2*k^2*z - 4*b^2*m*w*z + 4*B^2*m*w*z + B*a^2*ww*z - 2*A*a^2*k*z + A*a^2*z - a^2*b*w*z + 4*AA*a*b*k*m + 4*A*B*a*k*m - 4*AA*a*b*m - 4*A*B*a*m + 4*a*b^2*m*ww + a^3*b*k*ww - 4*B^2*a*m*ww + B*a^3*w - 2*AA*a^3*k - B*a^3*k*w + AA*a^3*k^2 - a^3*b*ww + AA*a^3, z)[1]

when I use numbers for parameters I got solution but I need a equation.

Thank in advance

[Rik]

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