P是以F1、F2为焦点的椭圆上一点,过焦点F2作∠F1PF2内角平分线的垂线...答:过焦点F2作∠F1PF2内角平分线的垂线,垂足为M,设F2M交PF1于Q,则F2M=MQ,向量PM*F2M=(x-acosu,y-bsinu)*(x-c,y)=(x-acosu)(x-c)+y(y-bsinu)=x^2+y^2-(acosu+c)x-bysinu+accosu=0,① Q(2x-c,2y)与P,F1共线,bsinu/(acosu+c)=2y/(2x-c+c)=y/x,所以sinu=y(...
点P是椭圆x^2/25 + y^2/16 =1上一点,F1,F2是椭圆的两个焦点答:a^2=25,a=5,c^2=a^2-b^2=25-16=9,c=3,内切圆半径r=1 (面积算法:三角形三边长分别为a,b,c,内接圆半径为r,则三角形面积=(a+b+c)r*1/2)△PF1F2面积=[|PF1|*r+|PF2|*r+|F1F2|*r]*1/2 =r/2*(2a+2c)=r(a+c)=1*(5+3)=8 而:△PF1F2面积=1/2*|F1F2|...