亲们,求支援.,亲们,求支援.累呗 ,
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亲们,求支援.,
亲们,求支援.累呗 ,
![](http://img.wesiedu.com/upload/0/90/090397dbcfc3dca711fd639f65e0452f.jpg)
亲们,求支援.累呗 ,
![](http://img.wesiedu.com/upload/0/90/090397dbcfc3dca711fd639f65e0452f.jpg)
![亲们,求支援.,亲们,求支援.累呗 ,](/uploads/image/z/20172869-53-9.jpg?t=%E4%BA%B2%E4%BB%AC%2C%E6%B1%82%E6%94%AF%E6%8F%B4.%2C%E4%BA%B2%E4%BB%AC%2C%E6%B1%82%E6%94%AF%E6%8F%B4.%E7%B4%AF%E5%91%97%26nbsp%3B%2C)
1.离心率=√2/2
2a=4√2
a=2√2
M:x^2/8+y^2/4=1
2.存在
设y=kx+m,
y=kx+m与x^2/8+y^2/4=1联立
∴(1+2k^2)x^2+4kmx+2m^2-8=0
当△=8(8k^2-m^2+4)>0
x1+x2=-4km/(1+2k^2)
x1x2=(2m^2-8)/(1+2k^2)
y1y2=(m^2-8k^2)/(1+2k^2),
OA⊥OB
∴x1x2+y1y2=0
∴3m^2-8k^2-8=0
∴ k^2=(3m^2-8)/8≥0
又 8k^2-m^2+4>0
∴ m^2>2,3m^2≥8
∴ m≥2√6/3或m≤-2√6/3
又y=kx+m与圆心在原点的圆相切
∴ r=|m|/(√1+k^2), r=2√6/3
∴ x2+y2=8/3
K不存在时,切线为 x=±2√6/3,交点( 2√6/3, ±2√6/3)或( -2√6/3, ±2√6/3),
∵ |AB|=1+k2|x1-x2|
k≠0时, |AB|=√32/3(1+1/4k4+1k2+4)
∴ 4√6/3<|AB|≤2√3(当 k=±√2/2时取等)
k=0时, |AB|=4√3/6
k不存时, |AB|=4√3/6
∴ |AB|∈[4√3/6,2√3]
http://zhidao.baidu.com/question/524134366.html
2a=4√2
a=2√2
M:x^2/8+y^2/4=1
2.存在
设y=kx+m,
y=kx+m与x^2/8+y^2/4=1联立
∴(1+2k^2)x^2+4kmx+2m^2-8=0
当△=8(8k^2-m^2+4)>0
x1+x2=-4km/(1+2k^2)
x1x2=(2m^2-8)/(1+2k^2)
y1y2=(m^2-8k^2)/(1+2k^2),
OA⊥OB
∴x1x2+y1y2=0
∴3m^2-8k^2-8=0
∴ k^2=(3m^2-8)/8≥0
又 8k^2-m^2+4>0
∴ m^2>2,3m^2≥8
∴ m≥2√6/3或m≤-2√6/3
又y=kx+m与圆心在原点的圆相切
∴ r=|m|/(√1+k^2), r=2√6/3
∴ x2+y2=8/3
K不存在时,切线为 x=±2√6/3,交点( 2√6/3, ±2√6/3)或( -2√6/3, ±2√6/3),
∵ |AB|=1+k2|x1-x2|
k≠0时, |AB|=√32/3(1+1/4k4+1k2+4)
∴ 4√6/3<|AB|≤2√3(当 k=±√2/2时取等)
k=0时, |AB|=4√3/6
k不存时, |AB|=4√3/6
∴ |AB|∈[4√3/6,2√3]
http://zhidao.baidu.com/question/524134366.html