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众所周知,要求经过一般二次曲线C: Ax~2+Bxy+Cy~2+Dx+Ey+F=0上一点p(x_1,y_1)的切线方程,可以应用如下的代换法则: (1) 用x_1x和y_1y分别代换方程中的x~2和y~2:
It is well known that the following tangent equation is required to pass the generalized quadratic curve C: Ax~2+Bxy+Cy~2+Dx+Ey+F=0 at a point p(x_1,y_1). The following substitution rule can be applied: (1) Replace x~2 and y~2 in the equations with x_1x and y_1y: