恒等式2(a2+b2)=[(a+b)2+(a-b)2] (a,b∈R)是中学数学中的一个重要公式,由此 恒等式可得出如下性质: 2(a2+b2)≥(a+b)2(*)(当a=b时取等 号). 经笔者探究,运用这一性质解(证)有关不 等式问题,思路清晰,简捷明快,能收到事半功 倍之效.下面用(*)解答三道赛题: 1.已知x,y都在区间(-2,2)内,且xy= Identity 2(a2+b2)=[(a+b)2+(ab)2] (a,b∈R) is an important formula in middle school mathematics. From this identity, the following properties can be derived: 2(a2+ B2) ≥ (a + b) 2 (*) (take an equal sign when a = b). After the author explores, use this property to solve the problem of inequality, the thinking is clear, simple and clear, you can get twice the effort Effect. Use the following (*) to answer three races: 1. Know that x, y are within the interval (-2, 2), and xy =