过椭圆X^2/a^2+x^2/b^2=1(a>b>0)左焦点斜率为1的直线交椭圆于AB两点,且AF2,AB,BF2成等差数列.1求离心率2设点P(0,-1)满足PA=PB,求椭圆的方程.
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过椭圆X^2/a^2+x^2/b^2=1(a>b>0)左焦点斜率为1的直线交椭圆于AB两点,且AF2,AB,BF2成等差数列.1求离心率2设点P(0,-1)满足PA=PB,求椭圆的方程.
过椭圆X^2/a^2+x^2/b^2=1(a>b>0)左焦点斜率为1的直线交椭圆于AB两点,且AF2,AB,BF2成等差数列.1求离心率
2设点P(0,-1)满足PA=PB,求椭圆的方程.
过椭圆X^2/a^2+x^2/b^2=1(a>b>0)左焦点斜率为1的直线交椭圆于AB两点,且AF2,AB,BF2成等差数列.1求离心率2设点P(0,-1)满足PA=PB,求椭圆的方程.
AB+BF2+AF2=4a 2AB=AF2+BF2 所以AB=3/4a
AF1=ep/1-ecos45°
F1B=ep/1-ecos135°
AB=3/4a
P=b^2/c=a(1/e-e){椭圆的极坐标方程,P为以F1为极坐标原点到椭圆准线的距离}
e^2=1/2
A(x1,y1)
B(x2.y2)
M(x1+x2/2,y1+y2/2)
K1=1,K2=-1（PM直线的斜率)
设直线L：y=x+c
b^2x^2+a^2y^2=a^2b^2
x1+x2=-2a^2c/a^2+b^2, y1+y2=x1+x2+2c
K2=-1（PM直线的斜率),即y1+y2+x1+x2+2c=0
c^2/a^2=1/2,c=3
a^2=18
b^2=9
x^2/18+y^2/9=1
是X^2/a^2+x^2/b^2=1还是X^2/a^2+y^2/b^2=1
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