r=3.10
s=0.08
f=0.30

syms r s f x
eq= 0==-(r^2*(x-1)*((0.5*x)-1)+1+((s)/(1-x)))*x+f;
solve(eq,x)

% solve(root(r^2*z^4 - 4*r^2*z^3 + 5*r^2*z^2 + 2*z^2 - 2*r^2*z - 2*s*z - 2*f*z - 2*z + 2*f, z, 1)
%
% poly = [r^2 -4*r^2 (5*r^2)+2 (-2*r^2)-(2*s)-(2*f)-2 2*f];
%
% r=roots(poly)