14题.

C(xc,yc);AB点坐标先求；y=(x-1)/2代入y^2=4x得出x^2-18x+1=0即xa+xb=18;xaxb=1则ya+yb=18/2-1=8;ya*yb=(xaxb-(xa+xb)+1)/4=-4
垂直即斜率相乘为-1则(yc-yb)/xc-xb*(yc-ya)/(xc-xa)=-1转换为(yc-yb)（yc-ya）+(xc-xb)(xc-xa)=0化开式子yc^2-yc*8-4=xc^2-18xc+1又yc^2=4xc则解出xc,yc有两个解.