题干

变量x,y满足x=ty=21-t(t为参数),则代数式
y
+
2
x
+
2
的取值范围是____ 
上一题 下一题 0.0难度 选择题 更新时间:2017-05-21 02:09:39

答案(点此获取答案解析)

2
3
,2

同类题2

读课文《走马灯的奥秘》选段,回答问题。

  茅(máo)以升七岁那年,过元宵(xiāo)节的时候,家里买了两盏(zhǎn)棱(léngɡ)柱形的走马灯。一盏挂在墙壁上,一盏悬(xuán)在堂屋中央。

  走马灯像磁(cí)石一样,把茅以升吸引住了。他仰着头,目不转(zhuǎn)睛地盯着走马灯。只见走马灯中间有一个轴(zhóu),轴上有一个可以旋(xuán)转的小轮子,轴心插着红蜡烛(làzhú),轮子四周插着彩色的小纸人和小纸马。蜡烛点燃以后,轮子就旋转起来,轮子四周的小纸人和小纸马也跟着转zhuàn动。明亮的烛光把小纸人和小纸马的影子投在灯壁上,十分有趣。

  他越看越入迷。一连串(chuàn)的问题,争着往他脑子里挤:小纸人、小纸马怎么会转?怎么有时转得快,有时转得慢呢?……

  他带着这些问题去问大人。大人告诉他:“是蜡烛的热气熏(xūn)的。”他听了大人的话,就把挂在墙上的走马灯取下来,“噗(pū)”的一声,把蜡烛吹灭了。小纸人、小纸马越跑越慢,最后停了下来。

  “那么,怎样才能让小纸人、小纸马跑得快一些呢?”他又提出了一个新问题。大人告诉他:“热气大,小纸人、小纸马就跑得快。”于是,他又拿来一支蜡烛,把两支一齐点燃。果然,小纸人、小纸马飞快地转起来……

这天晚上,茅以升特别高兴。虽然他没有完全弄明白走马灯转动的科学道理,但科学的种子已经播进他幼(yòu)小的心灵。“我”是采取什么招数来赢得棋局的胜利的?请在课文中找出相关的语句。

同类题5

短文改错

下面短文中有10处语言错误。请在有错误的地方增加、删除或修改某个单词。

增加:在缺词处加一个漏字符号(∧),并在其下面写上该加的词。

删除:把多余的词用斜线(﹨)划掉。

修改:在错的词下画一横线,并在该词下面写出修改后的词。

注意:1.每处错误及其修改均仅限一词;

2.只允许修改10处,多者(从第11处起)不计分。


例如:

It was very nice to get your invitation to spent∧weekend with you. Luckily

the

I was completely free then, so I’ll to say “yes”. I’ll arrive in Bristol at around 8:00 p.m.

am

in Friday evening.

On


My old classroom was interesting because three side of the classroom were made from glass. I enjoyed sit close to the windows and looking at the view. On the left-hand side of the class, I could easy see the football field. In the mornings, it was full of students exercising. The view from the back of the classroom is also splendid. Close to the school there was a beautiful park with many trees around them. Farther in the distance, I could not enjoy the view of snowy mountains. On the right side of the class was the road. I was always interested to see the drivers in hurry in the morning. The position of the classroom with its view made me felt like I was dreaming. If I was only a child when I studied in that classroom, I will never forget it.

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