椭圆x²/9+y²/2=1的焦点为F1、F2,点P在椭圆上,则向量PF1*向量PF...答:由题设得 :c^2=9-2=7,c=√7.F1(-√7,0),F2(√7,0)设抛物线上的p(x,y),则 向量PF1=(-√7-x,-y);向量PF2=(√7-x,-y).向量PF1*向量PF2=(-√7-x)(√7-x)+(-y)(-y).=x^2-7+y^2∴向量PF1*向量PF2=X^2+y^2-7.---即为所求...
P(x,y)是椭圆x2/a2+y2/b2=1(a大于b大于0)上一点,F1,F2为椭圆的两个焦 ...答:设F1(-c,0),F2(c,0),P(acosu,bsinu),其中c=√(a^2-b^2),则 向量PF1=(-c-acosu,-bsinu),PF2=(c-acosu,-bsinu),∴PF1*PF2=(-c-acosu)(c-acosu)+(-bsinu)^2 =a^2(cosu)^2+b^2(sinu)^2-c^2 =a^2[1-(sinu)^2]+b^2(sinu)^2-c^2 =(b^2-a^2)(sin...