x²-ax+2＞0x²-ax＞-2x²-ax +a²/4＞-2+a²/4(x-a/2)²＞（a²-8）/4当-2√2＜a＜2√2时：x∈R当a=-2√2或a=2√2时：x≠a/2当a＜-2√2或a＞2√2时：x＜{a-√(a²-8)}/2，或x＞{a+√(a²-8)}/2
