1)焦點弦:A(x1,y1),B(x2,y2),AB為橢圓的焦點弦,M(x,y)為AB中點,則L=2a±2ex
(2)設直線:與橢圓交於P1(x1,y1),P2(x2,y2),且P1P2斜率為K,則|P1P2|=|x1-x2|√(1+K²)或|P1P2|=|y1-y2|√(1+1/K²)
雙曲線:
(1)焦點弦:A(x1,y1),B(x2,y2),AB為雙曲線的焦點弦,M(x,y)為AB中點,則L=-2a±2ex
(2)設直線:與雙曲線交於P1(x1,y1),P2(x2,y2),且P1P2斜率為K,則|P1P2|=|x1-x2|√(1+K²)或|P1P2|=|y1-y2|√(1+1/K²){K=(y2-y2)/(x2-x1)}
拋物線:
(1)焦點弦:已知拋物線y²=2px,A(x1,y1),B(x2,y2),AB為拋物線的焦點弦,則|AB|=x1+x2+p或|AB|=2p/(sin²H){H為弦AB的傾斜角}
(2)設直線:與拋物線交於P1(x1,y1),P2(x2,y2),且P1P2斜率為K,則|P1P2|=|x1-x2|√(1+K²)或|P1P2|=|y1-y2|√(1+1/K²){K=(y2-y2)/(x2-x1)}
1)焦點弦:A(x1,y1),B(x2,y2),AB為橢圓的焦點弦,M(x,y)為AB中點,則L=2a±2ex
(2)設直線:與橢圓交於P1(x1,y1),P2(x2,y2),且P1P2斜率為K,則|P1P2|=|x1-x2|√(1+K²)或|P1P2|=|y1-y2|√(1+1/K²)
雙曲線:
(1)焦點弦:A(x1,y1),B(x2,y2),AB為雙曲線的焦點弦,M(x,y)為AB中點,則L=-2a±2ex
(2)設直線:與雙曲線交於P1(x1,y1),P2(x2,y2),且P1P2斜率為K,則|P1P2|=|x1-x2|√(1+K²)或|P1P2|=|y1-y2|√(1+1/K²){K=(y2-y2)/(x2-x1)}
拋物線:
(1)焦點弦:已知拋物線y²=2px,A(x1,y1),B(x2,y2),AB為拋物線的焦點弦,則|AB|=x1+x2+p或|AB|=2p/(sin²H){H為弦AB的傾斜角}
(2)設直線:與拋物線交於P1(x1,y1),P2(x2,y2),且P1P2斜率為K,則|P1P2|=|x1-x2|√(1+K²)或|P1P2|=|y1-y2|√(1+1/K²){K=(y2-y2)/(x2-x1)}