y?=4x;
2、設過點k(1,0)的直線方程為 y=k(x-1),將之代入拋物線方程,整理得k?x?-2(k?+2)x+k?=0,
令點p(x1,y1),q(x2,y2),於是x1·x2=1,x1+x2=-2(k?+2)/k?.
原式=pq/pk*kq
=(x1+x2+2)/g[(1-x1)?+y1?]g[(1-x2)?+y2?)]{帶入y?=4x就能開方了}
=-4k?/(1+x1)(1+x2)
=-4k?/[2-2(k?+2)/k?]
=1(定值)