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问:已知x-y=3,x+y=7.求:x(x-y)-y(y-x)的值
人气:203 ℃ 时间:2020-09-30 23:49:03
解答
x(x-y)-y(y-x)
=x(x-y)+y(x-y)
=(x-y)(x+y)
=3×7
=21
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