令å线为y=kx+m
å°y=kx+m代å
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x^2/a+y^2/b=1ï¼å³bx^2+ay^2-ab=0å¾ï¼
bx^2+a(kx+m)^2-ab=0
(ak²+b)x^2+2akmx+am^2-ab=0
å¤å«å¼â³=0
(2akm)^2-4(ak^2+b)(am^2-ab)=0
(akm)^2-(ak^2+b)(am^2-ab)=0
(ak)m^2-(a^2k²+ab)m^2 +ab(ak^2+b)=0
-abm^2 +ab(ak^2+b)=0
m^2=(ak^2+b)
m=屉(ak^2+b)
y=kx-â(ak^2+b)ï¼æy=kx+â(ak^2+b)
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