Text Solve the biquadratic inequality x4−5x2+4≥0.x^4-5x^2+4\ge 0.x4−5x2+4≥0. Solution Set t=x2≥0t=x^2\ge 0t=x2≥0: the inequality becomes t2−5t+4≥0t^2-5t+4\ge 0t2−5t+4≥0, i.e. (t−1)(t−4)≥0(t-1)(t-4)\ge 0(t−1)(t−4)≥0, satisfied for t≤1t\le 1t≤1 or t≥4t\ge 4t≥4. t≤1t\le 1t≤1: x2≤1 ⟹ −1≤x≤1x^2\le 1\implies -1\le x\le 1x2≤1⟹−1≤x≤1; t≥4t\ge 4t≥4: x2≥4 ⟹ x≤−2 ∨ x≥2x^2\ge 4\implies x\le -2\ \vee\ x\ge 2x2≥4⟹x≤−2 ∨ x≥2. x≤−2 ∨ −1≤x≤1 ∨ x≥2.\boxed{x\le -2\ \vee\ -1\le x\le 1\ \vee\ x\ge 2.}x≤−2 ∨ −1≤x≤1 ∨ x≥2.