-x^3+x^2+4x-5=0

x^3 - x^2 - 4x + 5 = 0

no easy way, here is what Wolfram says
http://www.wolframalpha.com/input/?i=x%5E3+-+x%5E2+-+4x+%2B+5+%3D+0

try some kind of interation method or Newton's method using Calculus.