抛物线x方=4y,焦点F,过点p〔1,5〕的直线与抛物线交于AB两点,p恰好为ab...答:X^2=4Y,2p=4,p=2 则有焦点坐标是F(0,1).设A(X1,Y1),B(X2,Y2)则有AF=Y1+p/2,BF=Y2+p/2 故有AF+BF=Y1+Y2+p,又Y1+Y2=2*5=10 所以,AF+BF=10+2=12
已知F是抛物线X方=4Y的焦点,点P在抛物线上,M是线段PF的中点,若PF的决...答:x^2=4y=2py,则p=2,准线是y=-p/2=-1 设P坐标是(xo,yo),则PF=P到准线的距离=yo+1 设M坐标是(x',y'),则y'=(yo+0)/2=yo/2 又PF<=3,即yo+1<=3, yo<=2 故y'<=1,又y'>=0 即M纵坐标范围是0<=y'<=1