0≤x≤2 y＝1-x/2
F＝1/x+1/y＝1/x+2/﹙2-x﹚
F′＝-1/x²+2/﹙2-x﹚²＝[2x²-﹙2-x﹚²]/[x²﹙2-x﹚²]＝0 x＝2﹙√2-1﹚ y＝2-√2
1/x+1/y＝√2+3/2 ﹙最小值﹚