设切点坐标为P(x0,y0),
用隐函数求导,2x/6+2y*y'/3=0,
y'=-x/(2y),
在(x0,y0)处导数为:-x0/(2y0),
切线斜率k=(1-y0)/(4-x0)=-x0/(2y0),
x0^2+2y0^2=4x0+2y0,(1)
因P(x0,y0)点在椭圆上,
故x0^2/6+y0^2/3=1,
x0^2+2y0^2=6,(2)
对比(1)式和(2)式,
4x0+2y0=6,
2x0+y0=3,
y0=3-2x0,(3)
代入(2)式,3x0^2-8x0+4=0,
(3x0-2)(x0-2)=0,
∴x0=2/3,或x0=2,
y0=5/3,或y0=-1,
∴ 切线方程为:(y-5/3)/(x-2/3)=(-2/3)/(2*5/3)
即:3x+15y-27=0.
或,(y+1)/(x-2)=(-2/(-2)=1,
即:y=x-1.
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