3 x - 7*x
x^3 - 7*x
/ ___\ / ___\ x*\x + \/ 7 /*\x - \/ 7 /
(x*(x + sqrt(7)))*(x - sqrt(7))
/ 2\ x*\-7 + x /
x*(-7 + x^2)
x^3 - 7.0*x