Question 988411
the roots must be (x-3)^2 and (x+5)^2
That is (x2-6x+9) (x^2+10x+25)
That is 
x^4+10x^3+25x^2-150x+225
       -6x^3-60x^2+90x
                +9x^2
===
x^4+4x^3-26x^2-60x+225
{{{graph(300,300,-10,10,-1000,3000,x^4+4x^3-26x^2-60x+225)}}}