问题 解答题
设函数f(x)=-x3+3x+2分别在x1、x2处取得极小值、极大值.xOy平面上点A、B的坐标分别为(x1,f(x1))、(x2,f(x2)),该平面上动点P(x,y),Q(mx,2y),
OC
=
OQ
+m
OA
满足
AP
OC
=1-m

(1)求点A、B的坐标;
(2)求动点P的轨迹方程,并判断轨迹的形状.
答案

(1)令f'(x)=(-x3+3x+2)'=-3x2+3=0解得x=1或x=-1

当x<-1时,f'(x)<0;当-1<x<1时,f'(x)>0;当x>1时,f'(x)<0

所以,函数在x=-1处取得极小值,在x=1取得极大值,

故x1=-1,x2=1,f(-1)=0,f(1)=4

所以点A、B的坐标为A(-1,0),B(1,4);

(2)由题意,

AP
=(1+x,y),
OC
=(mx-m,2y)

AP
OC
=1-m

∴(1+x)(mx-m)+2y2=1-m

∴mx2+2y2=1

①m=0时,y=±

2
2
,表示两条平行直线;

②m=2时,x2+y2=

1
2
,表示原点为圆心,半径为
2
2
的圆;

③m<0时,

y2
1
2
-
x2
-
1
m
=1,表示焦点在y轴上的双曲线;

④m>0时,

y2
1
2
+
x2
1
m
=1,若0<m<2,表示焦点在x轴上的椭圆;若m>2,表示焦点在y轴上的椭圆.

不定项选择题
单项选择题

The United States is usually given credit for creating and developing the musical comedy as it is known today. The first musical shows were based (1) everyday American life and the (2) development of the form took place in the United States for more than half a century. (3) the early 1970s, (4) , the London theater has (5) the Broadway stage.

The Black Crook, which opened at Niblo’s Garden in New York City on Sept. 12, 1866, is usually (6) as the inspiration for musical comedy. A troupe of French ballet dancers (7) to be stranded in New York without work (8) a fire damaged the theater (9) they had been booked. In order to keep a (10) to them, the theater producer put the dancers into a melodrama written by Charles M. Barres.

The first stage production that was (11) a musical comedy was a show that was (12) from the Prince of Wales Theater to the Gaiety Theater in London in 1892. Staged by George Edwards, the show called In Town featured a chorus line of Gaiety Girls. The (13) year A Gaiety Girl was equally successful, and a (14) of the show played in New York in the same year. When it was (15) in newspapers, it was designated a musical comedy and regarded as a new (16) of entertainment.

It did not take the form long to (17) in the United States. Almost (18) one of the most renowned talents of the American stage went to work on his own musicals. The singer-dancer George M. Cohan staged Little Johnny Jones in 1904. Cohan, (19) own life story was made into the musical George M (1968), also wrote the books, words, and (20) for Forty-five Minutes from Broadway ( 1906 ), The Little Millionaire ( 1911 ), The Song and Dance Man ( 1923 ), and American Born (1925).

8()

A.because

B.thus

C.but

D.hence