众所周知,过二次曲线f(x,y)=0上一点T(x0,y0)的切线方程为f(x,y)=0中将x2换成x0x,y2换成y0y,xy换成(x0y+xy0)/2,x换成(x+x0)/2,y换成y02+y,其中f(x,y)=Ax2+Bxy+Cy2+Dx+Ey+F;过该二次曲线外一点P(x0,y0)引二次曲线两条切线的切点弦所在直线的方程形式同前·有趣的是以点P(x0,y0) As we all know, the tangent equation of the point T(x0, y0) at the point where the hyperbolic curve f(x,y)=0 is f(x,y)=0, x2 is replaced by x0x, y2 is replaced by y0y, and xy is replaced by X0y+xy0)/2, x is replaced by (x+x0)/2, y is replaced by y02+y, where f(x,y)=Ax2+Bxy+Cy2+Dx+Ey+F; over the quadratic curve The outer point P(x0,y0) leads to the tangent point of the two tangents of the quadratic curve. The equation of the line where the chord lies is the same as before. The interesting point is the point P(x0,y0).