设切点A(x2,y2),B(x3,y3),x2≠x3或y2≠y3,则切线
PA:x2x+y2y=1,
PB:x3x+y3y=1,
它们都过P(x1,y1),
∴x1x2+y1y2=1,
x1x3+y1y3=1,
∴点A,B都在直线x1x+y1y=1上,而两点确定一条直线,
∴AB的方程是x1x+y1y=1.
设切点A(x2,y2),B(x3,y3),x2≠x3或y2≠y3,则切线
PA:x2x+y2y=1,
PB:x3x+y3y=1,
它们都过P(x1,y1),
∴x1x2+y1y2=1,
x1x3+y1y3=1,
∴点A,B都在直线x1x+y1y=1上,而两点确定一条直线,
∴AB的方程是x1x+y1y=1.