Question 766857
u=x^4

2u^2+15u-27=0

2u^2+18u-3u-27=0

2u(u+9)-3(u+9)=0

(2u-3)(u+9)=0


but u+9 contributes no real roots


2u-3=0

u=3/2


x^4 = 3/2


x^2 = +- sqrt(3/2)


from which we use the principal root


thus 

{{{
x=  root(4,3/2)
}}}

or 

{{{
x= - root(4,3/2)
}}}