设椭圆方程为 x=acost,y=bsint椭圆外一点(x0,y0)与椭圆切于（x,y）点斜率k=-bcost/asint = (y0-bsint)/(x0-acost)化简得到bx0cost+ay0sint-ab = 0即 bx0x/a + ay0y/b -ab = 0 为切线方程 或者写的更好看一点x0x/a^2 ...