3x(9x^2-36x-36)-6(9x^2-36x-36)=0
27x^3-108x^2+108-54x^2+216x-216=0
(27x^3-162x^2+216x)=108
divide by 27
x^3-6x^2+8x=4
divide by x on the left side of the equa only
x^2-6x+8=4
(x+4)(x-2)=4
x+4 =4 or x+2=4
x=8 or x=2
(3x-6) (9x^2-36x+36)=0
(x-2) (x^2-4x+4)=0
(x-2) (x-2)^2=0
(x-2)^3=0
the above equation is of degree three and hence it is supposed to have three roots. And these three roots as appearing are real and equal and that root is 2.
Hence the roots of given equation is said to be 2,2,2.