> str="a!=0, x = -1/2 sqrt(b^2/(4 a^2) + (sqrt((-72 a c e + 27 a d^2 + 27 b^2 e - 9 b c d + 2 c^3)^2 - 4 (12 a e - 3 b d + c^2)^3) - 72 a c e + 27 a d^2 + 27 b^2 e - 9 b c d + 2 c^3)^(1/3)/(3 2^(1/3) a) + (2^(1/3) (12 a e - 3 b d + c^2))/(3 a (sqrt((-72 a c e + 27 a d^2 + 27 b^2 e - 9 b c d + 2 c^3)^2 - 4 (12 a e - 3 b d + c^2)^3) - 72 a c e + 27 a d^2 + 27 b^2 e - 9 b c d + 2 c^3)^(1/3)) - (2 c)/(3 a)) + 1/2 sqrt(b^2/(2 a^2) - (-b^3/a^3 + (4 b c)/a^2 - (8 d)/a)/(4 sqrt(b^2/(4 a^2) + (sqrt((-72 a c e + 27 a d^2 + 27 b^2 e - 9 b c d + 2 c^3)^2 - 4 (12 a e - 3 b d + c^2)^3) - 72 a c e + 27 a d^2 + 27 b^2 e - 9 b c d + 2 c^3)^(1/3)/(3 2^(1/3) a) + (2^(1/3) (12 a e - 3 b d + c^2))/(3 a (sqrt((-72 a c e + 27 a d^2 + 27 b^2 e - 9 b c d + 2 c^3)^2 - 4 (12 a e - 3 b d + c^2)^3) - 72 a c e + 27 a d^2 + 27 b^2 e - 9 b c d + 2 c^3)^(1/3)) - (2 c)/(3 a))) - (sqrt((-72 a c e + 27 a d^2 + 27 b^2 e - 9 b c d + 2 c^3)^2 - 4 (12 a e - 3 b d + c^2)^3) - 72 a c e + 27 a d^2 + 27 b^2 e - 9 b c d + 2 c^3)^(1/3)/(3 2^(1/3) a) - (2^(1/3) (12 a e - 3 b d + c^2))/(3 a (sqrt((-72 a c e + 27 a d^2 + 27 b^2 e - 9 b c d + 2 c^3)^2 - 4 (12 a e - 3 b d + c^2)^3) - 72 a c e + 27 a d^2 + 27 b^2 e - 9 b c d + 2 c^3)^(1/3)) - (4 c)/(3 a)) - b/(4 a)"
> Wolfram2R(str,2) |> eval()
[1] 0.618034

今のところうまく動作している。