Factor x^3-5x^2-50x/x^4+10x^3

x^3-5x^2-50x/x^4+10x^3

should have been properly parenthesized as follows:
(x^3-5x^2-50x)/(x^4+10x^3)
Start with the factors common to all terms in each of numerator(x) and denominator (x³):
x(x²-5x-50)/(x³(x+10))
Now factorize the quadratic expression of the numerator:
(x(x+10)(x-5))/(x³(x+10))
Cancel common factors, stipulating that x≠0 and x≠-10,
(x-5)/x²