solve for x, x^6-19x^3-216=0

Question

1.solve for x, x^6-19x^3-216=0

Answer 1

x⁶-19x³-216=0

Let y=x³ and have

y²-19y-216=0 which may be factored as

(y-27)(y+8)=0 which gives that

y=27, y=-8 and so that

x=3 or x=-2