质量为m的物体用轻绳AB悬挂于天花板上。用水平向左的力F缓慢拉动_爱下问搜题

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质量为m的物体用轻绳AB悬挂于天花板上。用水平向左的力F缓慢拉动绳的中点O，如图所示。用T表示绳OA段拉力的大小，在O点向左移动的过程中（）

A.F逐渐变大，T逐渐变大

B.F逐渐变大，T逐渐变小

C.F逐渐变小，T逐渐变大

D.F逐渐变小，T逐渐变小

答案

参考答案：A

完形填空

完形填空。

     Do you know Eskimos (爱斯基摩人)? Let me tell you something about their life.
     The Eskimos live near the North Pole (北极). There are only two seasons there: winter and summer.
There is no spring _1_ autumn there. In winter nights are long. You can't _2_ the sun for more than two
months, even at noon. In summer days are long. For more than two months, the sun never _3_ and there
is no night.
     Eskimos have _4_ clothes. They make their clothes from the skins of animals (动物的皮). From
skins they make coats, hats and _5_. Near the North Pole trees can't grow, for it is _6_there. The
Eskimos _7_ make their houses from skins, stones (石头) or snow. When they go out in a storm (风暴)
and can't get back _8_, they make houses of snow. They leave these snow houses when the storm is
_9_.
     Life is _10_ for the Eskimos, but they still like to live there.

( )1.A. and
( )2.A. look
( )3.A. comes out
( )4.A. warm
( )5.A. food
( )6.A. too cold
( )7.A. like
( )8.A. from home
( )9.A. going
( )10.A. hard

B. not
B. look at
B. comes over
B. cold
B. drinks
B. too hot
B. have to
B. home
B. leaves
B. hardly

C. or
C. watch
C. goes down
C. cotton
C. medicine
C. either cold or hot
C. want
C. to home
C. over
C. easy

D. either
D. see
D. goes up
D. silk
D. shoes
D. not so cold
D. should
D. at home
D. on
D. easily

解答题

由多项式的乘法法则知：若（x+a）（x+b）=x²+x+q，则p=a+b，q=a·b；反过来x²+x+q=（x+a）（x+b）要将多项式x²+x+q进行分解，关键是找到两个数a、b，使a+b=p，a·b=q，如对多项式x²-3x+2，有p=-3，q=2，a=-1，b=-2。此时（-1）+（-2）=-3，（-1）（-2）=2，所以x²-3x+2可分解为（x-1）（x-2）即x²-3x-2=（x-1）（x-2）。
（1）根据以上填写下表：

多项式	p	q	a	b	分解结果
x²+9x+20
x²-9x+20
x²+x-20
x²-x-20

（2）根据填表，还可得出如下结论：
当q是正数时，应分解成两个因数a、b_______________号，a、b的符号与__________相同；
当q是负数时，应分解成的两个因数a、b______________号，a、b中绝对值较大的因数的符号与_______相同。
（3）分解因式：
x²-x-12=_____________；x²-7x+6=________________。