已知抛物线y=x^2-(k+3)x+2k-1···急!

题目

已知抛物线y=x^2-(k+3)x+2k-1···急!
已知抛物线y=x^2-(k+3)x+2k-1.
问：设抛物线与x轴交于A,B两点（A在B的左边）,顶点为C,C的纵坐标为m,求AB^2/m的值?

答案

设A（x1,0）,B(x2,0)由已知条件可得：C((k+3)/2,m)将点C坐标代入方程得:[(k+3)/2]^2-(k+3)*(k+3)/2+2k-1=m化简得：(k+3)^2-8k+4=-4mAB^2=(x2-x1)^2=(x1+x2)^2-4x1x2=(k+3)^2-4(2k-1)=(k+3)^2-8k+4=-4m所以AB^2/m=-4m...