[latex]x^4-10x^2 extless -9\ x^4-10x^2+9 extless 0\ x^4-x^2-9x^2+9 extless 0\ x^2(x^2-1)-9(x^2-1) extless 0\ (x^2-9)(x^2-1) extless 0\ (x-3)(x+3)(x-1)(x+1) extless 0\ xin(-3,-1)cup(1,3) [/latex]

x^4-10x^2<-9 x^4-10x^2+9<0 x^4-x^2-9x^2+9<0 x^2(x^2-1)-9(x^2-1)<0 (x^2-9)(x^2-1)<0  now for this to be true, the expressions must have different signs, so that the product is negative... x<±3 and x>±1 ±1