问题 解答题

已知命题p:点P的坐标为(x,y),点F1、F2的坐标分别是(-1,0)、(1,0),命题q:直线PF1、PF2的斜率分别是k1、k2,k1•k2=m(m∈R),p∧q真.

(Ⅰ)求点P的轨迹方程;

(Ⅱ)指出点P的轨迹类型(如圆、抛物线、直线等).

答案

(Ⅰ)由题意得,k1=

y
x+1
k2=
y
x-1

∵k1•k2=m(m∈R),∴

y
x+1
y
x-1
=m,

所以所求轨迹方程是:mx2-y2=m(m∈R,x≠±1).…4分

(Ⅱ)由(Ⅰ)点P的轨迹方程为mx2-y2=m(m∈R,x≠±1),

当m<0且m≠-1时,方程可化为 x2+

y2
-m
=1(x≠±1),∴P的轨迹是椭圆(除去与x相交的项点);

当m=-1时,方程x2+y2=1(x≠±1),∴P的轨迹是圆(除去与x的交点);

当m=0时,方程是y=0(x≠±1),∴P的轨迹是x轴(除去(-1,0)和(1,0)两点);

当m>0时,方程可化为x2-

y2
m
=1(x≠±1),∴P的轨迹是双曲线(除去项点)…12分.

单项选择题
阅读理解

The South Pole is a particular place on the earth.When people stand at the top of it looking around,they will find all directions face to north.No matter how they make their first step in which direction,they will always walk towards the north.That’s to say,only north and south exist there,neither east nor west exists.

At the top of the South Pole,any clock or watch keeps good time because all meridians(子午线) join there.All kinds of local time are completely suitable there.It is even difficult to distinguish(区别) New Year’s Eve from New Year’s Day.

The explorers and scientists from different countries always fix the time according to their own.Therefore the time by their watches was different when the people with different nationality gathered there.

The Winter Solstice(冬至日) is an important festival at the South Pole.It is always on June 21 or 22.This day is called Midwinter Festival,on which the daytime is the shortest in a year and the night the longest.All people at the South Pole extend greetings to each other and present gifts to each other.They usually give all kinds of celebrations.From that day on,the daytime will get longer day by day.

小题1:At the top of the South Pole,your watch will ________.

A.keep good time

B.be five minutes fast

C.stop

D.be ten minutes slow小题2:The Winter Solstice is an important festival ________.

A.in the world

B.at the South Pole

C.at the North Pole

D.in China小题3:On the Winter Solstice,________ is the shortest in a year.

A.the night

B.the noon

C.the morning

D.the daytime