y^2=2px,过焦点直线交抛物线于A(x1,y1)和B(x2,y2)两点,则AB弦长=x1+x2+pd=√(1+k)|x1-x2|=√(1+k)[(x1+x2)2 - 4x1x2] = √(1+1/k)|y1-y2| = √(1+1/k)[(y1+y2)2- 4y1y2]d =√[(1+k)△/a;] =√(1+k;)√(△)/|a|...