houbiao6100
幼苗
共回答了18个问题采纳率:94.4% 举报
(2/3x-y)(2/3x+y)=(2/3X)²-y²=4/9x²-y²
(xy+1)(xy-1)=(xy)²-1²=x²y²-1
(2a-3b)(3b+2a)=(2a)²-(3b)²=4a²-9b²
(-2b-5)(2b-5)=-[(2b)²-5²]=-[4b²-25]=25-4b²
2001*1999=(2000+1)(2000-1)=2000²-1=4000000-1=3999999
998*1002=(1000-2)(1000+2)=1000²-2²=1000000-4=999996
1年前
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