Question

решить: x$x^{6}-7x^{3} -8=0$

Answer 1

x^6 - 7x^3 - 8 = 0 

x^3 = t ==>
t^2  - 7t - 8 = 0 
D = 49 + 32 = 81 = 9^2
t1 = ( 7 + 9)/2 = 8
t2 = ( 7 -  9)/2 = - 1

x^3 = 8 
x = 2

x^3  = - 1
x = - 1 

Ответ
- 1 ; 2