(x`2 - 6x) (x`2 - 6x + 4) - 5 = 0
(x`2 - 6x)=t
t(t+4)-5=0
t^2+4t-5=0
t1=-5 (x`2 - 6x)=-5 x^2-6x+5=0 x1=5 x2=1
t2=1 (x`2 - 6x)=1 x^2-6x-1=0 D=40 x3=(6-2V10)/2=3-V10 x4=3+V10