yukiqeng
幼苗
共回答了18个问题采纳率:94.4% 举报
1 4/a²+1/b²=1,a²=b²+c²,c/a=√2/2.,
a=6,b=3.
x²/6+y²/3=1.
2 设ly=k(x-3),
y=k(x-3),x²/6+y²/3=1
(1+2k²)x²-12k²x+18k²-6=0.
设M,N为(x1,y1),(x2,y2),
x1+x2=12k²/1+2k²,x1x2=18k²-6/1+2k²,
y1=k(x1-3),y2=k(x2-3).
kAM+kAN= y1-1/x1-2+y2-1/x2-2
= (kx1-3k-1)(x2-2)+(kx2-3k-1)(x1-2)/(x1-2)(x2-2)= 2kx1x2-(5k+1)(x1+x2)+12k+4/x1x2-2(x1+x2)+4
= 2k(18k²-6)-(5k+1)•12k²+(12k+4)(1+2k²)/18k²-6-24k²+4(1+2k²)= -4k²+4/2k²-2=-2.
kAM+kAN为定值-2.
1年前
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