Question

椭圆X2/a2+y2/b2=1在点（x0,y0）处的切线方程为xx0/a2+yy0/b2=1,为什么?

Answer 1

椭圆为x^2/a^2+y^2/b^2=1,切点为(m,n),则m^2/a^2+n^2/b^2=1 --(1).对椭圆求导得y'=-b^2x/a^2y,即切线斜率k=-b^2m/a^2n,故切线为y-n=-b^2m/a^2n*(x-m),以(1)代入并化简得切线为mx/a^2+ny/b^2=1.