题目

x、y是实数，p=x2+2xy+2y2+2x+4y+5,则p的值（    ）A.恒为正数且有最小值3                     B.恒为正数且有最小值1C.恒为非负数且有最小值0                   D.恒为非负数且无最小值 答案：解析：p=x2+2xy+2y2+2x+4y+5=x2+2(y+1)x+(y+1)2+y2+2y+4=［x+(y+1)］2+(y+1)2+3≥3.答案：A

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