已知曲线C1:ρcos(θ+
(1)试判断曲线C1与C2的交点个数; (2)若过点M(1,0)直线l与曲线C2交于两个不同的点A,B,求
|
(1)由ρcos(θ+
)=π 4
,得2 2
ρ(cosθ-sinθ)=2 2
,2 2
所以x-y=1,
由ρ2=
,得ρ2(3-2cos2θ)=3,3 2-cos2θ
所以3(x2+y2)-2x2=3,即x2+3y2=3,
由
得2x2-3x=0,解得x=0或x=x-y=1 x2+3y2=3
,3 2
所以曲线C1与C2的交点有两个;
(2)①当直线l存在斜率时,设l的方程为y=k(x-1),A(x1,y1),B(x2,y2),
由
得(1+3k2)x2-6k2x+3k2-3=0,y=k(x-1) x2+3y2=3
△=36k4-4(1+3k2)(3k2-3)>0,即2k2+1>0恒成立,
则x1+x2=
,x1x2=6k2 1+3k2
,3k2-3 1+3k2
|MA|=
|x1-1|,|MB|=1+k2
|x2-1|,|AB|=1+k2
|x1-x2|,1+k2
=|MA|•|MB| |AB|
=(1+k2)|x1-1||x2-1|
|x1-x2|1+k2
|x1x2-(x1+x2)+1|1+k2 |x1-x2|
=
=
|1+k2
-3k2-3 1+3k2
+1|6k2 1+3k2 (
)2-6k2 1+3k2 4(3k2-3) 1+3k2
•6 6
=k2+1 k2+ 1 2
•6 6
,1+ 1 2k2+1
又k2≥0,所以
<6 6
≤|MA|•|MB| |AB|
•6 6
=2
;3 3
②当直线l不存在斜率时,把x=1代入x2+3y2=3得y=±
,6 3
此时
=|MA|•|MB| |AB|
=(
)26 3 2 6 3
,6 6
综合①②得
的取值范围为[|MA|•|MB| |AB|
,6 6
].3 3