椭圆(x²/25)+(y²/9)=1.即9x²+25y²=225.设直线4x-5y+t=0是椭圆的切线,该直线与4x-5y+40=0平行.联立消去y,得25x²+8tx+t²-225=0.⊿=64t²-100(t²-225)=0.===>t=±25.∴椭圆的切...