I don't know where you got "x= 0, x= 6, or x=-6" but 6 and -6 are obviously NOT solutions. If x= 6, for example, then so while [tex]\sqrt{6}= 2.44945 so , not 0. Did you mean "x= 0, , or "?

so let and the equation becomes . That can be factored as . Therefore, we have u= 0 or or . The 5 solutions to this fifth degree equation are x= 0, , , , and .