Answer :
x6 – 9x3 + 8 = 0
let u = x^3
u^2 - 9u + 8 = 0
(u-8)(u-1) = 0
u = 1,8
back substitute
1 = x^3
8 = x^3
x = 1 , 2
let u = x^3
u^2 - 9u + 8 = 0
(u-8)(u-1) = 0
u = 1,8
back substitute
1 = x^3
8 = x^3
x = 1 , 2