In order to solve $ \color{blue}{ 5x^{5}+12x^{2}+11x = 0 } $, first we need to factor our $ x $.
$$ 5x^{5}+12x^{2}+11x = x \left( 5x^{4}+12x+11 \right) $$$ x = 0 $ is a root of multiplicity $ 1 $.
The remaining roots can be found by solving equation $ 5x^{4}+12x+11 = 0$.
This polynomial has no rational roots that can be found using Rational Root Test.
Roots were found using quartic formulas