Please be clearer about the order of operations
x^2/3 can mean (x^2)/3 or x^(2/3)
If you meant x^(2/3), then the answer is as follows:
x^(2/3) = 8x
x^(2/3) - 8x = 0
( x^(2/3) )( 1 - 8x^(1/3) ) = 0
so either x^(2/3) = 0
or (1-8x^(1/3) ) = 0
which means:
x^(2/3) = 0
x = 0
--or--
1 - 8x^(1/3) = 0
1/8 = x^(1/3)
(1/8)^3 = ( x^(1/3) )^3
1/512 = x