|ax+2|≥|2x+b|.|ax+2|²≥|2x+b|².a²x²+4ax+4≥4x²+4bx+b².(a²-4)x²+4(a-b)x+(4-b²)≥0.a²-4＞0且⊿=16(a-b)²-4(a²-4)(4-b²)≤0.|a|＞2且ab=4....