I Am In Class 9

Please Help Me With My Doubts

If x = 1+5^1/3+5^2/3 then find the value of x³-3x²-12x+6

its actually a geometric progression

x = (24/(5^1/3 - 1))

put it in the expression

.....

its too wierd i beilive!!

(x-1)^3=5+25 + 3.5(x-1)
then simplyfy

we know x=1+5^1\3+5^2\3

then we have x-1=a+a^2 where a=5^1\3

then put (x-1)^3=a+a^2

and solve