先化简，再求值．xy+9y2-2[4xy-（3y2-x2y）]+5（-3y2+2

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问题解答题

先化简，再求值．xy+9y²-2[4xy-（3y²-x²y）]+5（-3y²+

x2y），其中x=1，y=-2．

答案

原式=xy+9y²-8xy+12y²-2x²y-15y²+2x²y

=21y²-7xy；

当x=1，y=-2时，原式=56．

选择题

We don't have ____ homework to do today, but we have ____ books to read. [ ]

A. too many; too much

B. too much; too many

C. too many; much too

D. much too; many too

判断题

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