wfish水煮鱼
幼苗
共回答了19个问题采纳率:94.7% 举报
(1)由已知c=3,准线得a^2/c=4/3,a=2,a^2+b ^2=c^2,b^2=9-4=5
x^/4-y^2/5=1
(2)设P(s,t),则有s^2/4-t^2/5=1,有s^2-4=(4/5)t^2(*)
设lF1P:y=t/(s+2)*(x+2),令x=4/3,则y=(10/3)t/(s+2),M(4/3,(10/3)t/(s+2))
设lF2P:y=t/(s-2)*(x-2),令x=4/3,则y=(-2/3)t/(s-2),N(4/3,(-2/3)t/(s-2))
F1M=(13/3,(10/3)t/(s+2))
F2N=(-5/3,(-2/3)t/(s+2))
F1M*F2N=-65/9-(20/9)t^2/(s^2-4)(将*式代入)=-65/9-(20/9)/(4/5)=-10为定值
1年前
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