7.29^2－2.71^2
=(7.29+2.71)(7.29-2.71)
=10*4.58
=45.8
xy＝1,x+y＝3,
则x^2y+xy^2 ＝xy(x+y)
=1*3
=3
j(1)简便计算：7.29^2－2.71^2＝ （2）已知xy＝1,x+y＝3,则x^2y+xy^2 ＝
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