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(2/3x-y)(2/3x+y)(xy+1)(xy-1)(2a-3b)(3b+2a)(-2b-5)(2b-5)2001*1999998*1002这几道题怎么做?求大神解答...
(2/3x-y)(2/3x+y)
(xy+1)(xy-1)
(2a-3b)(3b+2a)
(-2b-5)(2b-5)
2001*1999
998*1002这几道题怎么做?求大神解答!谢谢!秒好评! 展开
(xy+1)(xy-1)
(2a-3b)(3b+2a)
(-2b-5)(2b-5)
2001*1999
998*1002这几道题怎么做?求大神解答!谢谢!秒好评! 展开
1个回答
展开全部
(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
(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
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