已知过抛物y^2=2px的焦点F的直线交抛物线于A(X1,Y1)B(X2,Y2)(1)求证X1X2为定值(2)1/FA+
来源:学生作业帮 编辑:大师作文网作业帮 分类:数学作业 时间:2024/09/27 08:12:36
已知过抛物y^2=2px的焦点F的直线交抛物线于A(X1,Y1)B(X2,Y2)(1)求证X1X2为定值(2)1/FA+1/FB为定值
1)
AB直线方程为:y=k(x-p/2)
代人:y^2=2px得:
k^2(x-p/2)^2=2px
k^2x^2-(pk^2-2p)x+k^2p^2/4=0
x1x2=p^2/4
是定值
2)
FA^2=(x1-p/2)^2+y1^2
=x1^2-px1+p^2/4+2px1
=x1^2+px1+p^2/4
=(x1+p/2)^2
FA=x1+p/2
同样可得:FB=x2+p/2
1/FA+1/FB
=1/(x1+p/2)+1/(x2+p/2)
=(x1+x2+p)/(x1+p/2)(x2+p/2)
=(x1+x2+p)/(x1x2+p(x1+x2)/2+p^2/4)
=(x1+x2+p)/(p^2/4+p(x1+x2)/2+p^2/4)
=(x1+x2+p)/(p(x1+x2+p)/2)
=2/p
为定值
AB直线方程为:y=k(x-p/2)
代人:y^2=2px得:
k^2(x-p/2)^2=2px
k^2x^2-(pk^2-2p)x+k^2p^2/4=0
x1x2=p^2/4
是定值
2)
FA^2=(x1-p/2)^2+y1^2
=x1^2-px1+p^2/4+2px1
=x1^2+px1+p^2/4
=(x1+p/2)^2
FA=x1+p/2
同样可得:FB=x2+p/2
1/FA+1/FB
=1/(x1+p/2)+1/(x2+p/2)
=(x1+x2+p)/(x1+p/2)(x2+p/2)
=(x1+x2+p)/(x1x2+p(x1+x2)/2+p^2/4)
=(x1+x2+p)/(p^2/4+p(x1+x2)/2+p^2/4)
=(x1+x2+p)/(p(x1+x2+p)/2)
=2/p
为定值
已知过抛物y^2=2px的焦点F的直线交抛物线于A(X1,Y1)B(X2,Y2)(1)求证X1X2为定值(2)1/FA+
过抛物线y^2=2px(p大于0)的焦点作一条直线交抛物线于A(x1,y1)B(x2,y2)则y1y2/x1x2 为(
已知抛物线y=x2,直线l过抛物线的焦点且与抛物线分别交于A(x1,y1),B(x2,y2)两点 (1)求证:x1x2=
抛物线y^2=4x的焦点为f,过f的直线交抛物线于a(x1,y1),b(x2,y2)两点,则y1y2/x1x2=
已知直线l过抛物线y*2=2px(p〉0)的焦点,并且与抛物线交于A(x1,x2)和B (y1,y2)两点 (1)求证y
设抛物线的方程y^2=2px(p>0),过抛物线焦点的直线交抛物线于A(x1,y1)B(x2,y2)
已知抛物线y^2=2px(p>0)的焦点,斜率为2√2的直线交抛物线于A(x1,y1),B(x2,y2)(x1
已知抛物线方程为y2=2px(p>0),过焦点F的直线l与抛物线交于A(x1,y1)、B(x2,y2),AA1、BB1垂
过抛物线y^2=2px(p>0)的焦点作一条直线交抛物线与A(x1,y1),B(x2,y2),则y1y2/x1x2为多少
过抛物线y^2=2px(p>0)的焦点作一条直线交抛物线与A(x1,y1),B(x2,y2),则y1y2/x1x2的值是
设抛物线C:y^2=2px(p>0)的焦点为F,经过F的动直线l交抛物线C于A(x1,y1),B(x2,y2)两点,且y
已知过抛物线y^2=2px(p>0)的焦点 斜率为2根号2的直线交抛物线于A(x1,y1),B(x2,y2) -(x1