f(x) is defined for x12−x9+x4−x+1>0 ⇒ x4(x8+1)−x(x8+1)+1>0 ⇒ (x8+1)x(x3−1)+1>0 If x≥1 or x≤−1, then the above expres - sion is positive. If −1<x≤0, the above inequality still holds. If 0<x<1, then x12−x(x8+)+(x4+1)>0 ∵[x4+1>x8+1 and so x4+1>x(x8+1)] The domain of f=(−∞,∞)