已知x，y是方程组x+2y=4x-y=5的解，求代数式1+y-xx-2y÷x2-_爱下问搜题

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问题解答题

已知x，y是方程组

x+2y=4

x-y=5

的解，求代数式1+

y-x

x-2y

÷

x2-y2

x2-4xy+4y2

的值．

答案

解方程组

x+2y=4

x-y=-5

得：

x=-2

y=3

，

原式=1-

x-y

x-2y

•

(x-2y)2

(x+y)(x-y)

，

=1-

x-2y

x+y

，

=

x+y-x+2y

x+y

，

=

3y

x+y

，

当x=-2，y=3时，原式=

3×3

-2+3

=9．

完形填空

The other day I decided to teach my son about the power of small acts of kindness. He had won some lollies(棒棒糖) in a prize machine in the local supermarket, so I asked him if he would like to   46  his prizes with another child. He hesitated(犹豫) for a while because he is a(n)   47  boy, but said yes after I   48  him a bit.
A father and his daughter were   49 . I approached the father and asked if my son could give his   50  a lolly that he had won. The father looked at me in   51  and was unsure what to say. I   52  explained that I was teaching my son about the power of kindness. Eventually he said it was okay.
53 , his daughter, who was looking at us sideways(侧向一边地),   54  accept the lolly! At this moment, my son was rather embarrassed(尴尬) and then he   55  to me, “We go to the same   56 , Mum.”
Rather than say sorry to my son for embarrassing him and give up this   57 , I put a couple of lollies into their shopping bags and   58  them a great day!
When we left the supermarket, I   59  to my son, “People in the world today are not so open to   60  because their thoughts and opinions have been   61  by the past. However, we can reshape their opinions by   62  small acts of kindness. So don’t be embarrassed. Hey, they may have been standoffish(冷淡的), but I’m sure we left them   63 , moved and inspired in some way. Not only that,   64  the young girl will probably remember you as the boy with a   65  heart when she comes across you at school!”

D．blamed(责备)

B．out of sight

D．difficultly

A．Therefore(因此)

A．shouldn’t

B．whispered(小声说)

A．disappointed

问答题简答题

再障的鉴别诊断是什么？