已知：x2+y2=2，xy=-12，求代数式：（2x2-y2-3xy）-（x2-_爱下问搜题

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问题解答题

已知：x2+y2=2，xy=-

1

2

，求代数式：（2x²-y²-3xy）-（x²-2y²+xy）的值．

答案

（2x²-y²-3xy）-（x²-2y²+xy）

=2x²-y²-3xy-x²+2y²-xy

=x²+y²-4xy，

当x2+y2=2，xy=-

1

2

时，原式=2-4×

1

4

=2-2=0．

完形填空

完形填空（共12分，每小题1分）
阅读下面的短文，掌握其大意，然后从短文后各题所给的A、B、C、D四个选项中，选择最佳选项。
Haircuts from the Heart

Even though Rebecca didn't enjoy having long hair, still, month after month for two and a half years, Rebecca let her hair grow until it nearly reached her waist. At the right time, 1   would donate（捐献）her beautiful hair to a group in Palm Springs, Florida called Locks of Love.
Locks of Love is a special   2 called a charity(慈善机构). The members of this group work to help others in need.   3  the healthy cut hair that Rebecca sends them, they will have a wig(假发) made for a child who needs it. Children who need wigs are those who   4   all their hair because of illness or as a side effect from certain medicines they have to   5  . Rebecca's hair will be used to help replace the   6   that another child has lost. It will also replace some of the bad feelings that child may have from not having hair.
The day finally came to cut her long hair. Rebecca had chosen a beauty 7   in her city that gave to the Locks of Love program. The hairstylist who worked there took the time to make sure Rebecca's hair was cut and packaged properly .
First the hairstylist made sure that Rebecca's hair was clean, dry, and not damaged by chemicals. The hairstylist also made sure that the cut hair would be at least ten inches long. Then he cut Rebecca's hair. Rebecca had   8   to have her cut hair bundled into a ponytail（绑成马尾辫）. She took great   9   in placing the cut ponytail into a plastic bag and then an envelope to be mailed to Locks of Love. Finally as her reward, Rebecca's   10   hair was styled.
Now with short hair, Rebecca made another important decision. She decided to let it grow long again. 11   she will give it to Locks of Love. Judging from last time, she   12  it will take about three years. Even though Rebecca no longer has long hair, she certainly has a big heart.

A．organization	B．invitation
C．discussion	D．conversation

判断题

仔猪物质代谢旺盛，生长发育快，因此一生下就可以进行断奶，补充饲料进行饲喂是不会影响其成活率的。