(log2 x)^-1 +4log2 x^2 +9=0
log2 x=t
1/t+8t+9=0
1+8t^2+9t=0
[-9+-sqrt(81-32)]/16=[-9+-7]/16
t1=-1
t2=-1/8
log2 x=-1 x=1/2
log2 x=-1/8 x=-3