Question 1134044
factors can be +/-1,2,4,5,10,20
synthetic division
try 4 
4/1---3--- -14---- -20
  1   7    14-----  doesn't work
-5/1  -2    -4-----20 does work
so (x+5) is a factor and the remainder is from the quotient (x^2-2x-4), which needs the quadratic formula for
x=(1/2)(2+/-sqrt (4+16)) or 1+/- sqrt (5)
the numerical roots are -5,-1.236, 3.236,
{{{graph(300,300,-10,10,-10,10,x^3+3x^2-14x-20)}}}