æ¤åä¸ç´çº¿ç¸å,æ±æ¤åæ¹ç¨
æ¤åç¦ç¹ï¼-2,0ï¼ï¼2,0ï¼
ç´çº¿æ¹ç¨X+2Y=4
c²=4
å设为x²/a²+y²/(a²-4)=1
x=4-2y
代å
¥(a²-4)(16-16y+4y²)+a²y²=a^4-4a²
(5a²-16)y²-16(a²-4)y-a^4+20a²-64=0
å线åâ³=0
æ以256(a²-4)²+(20a²-80)(a^4-20a²+64)=0
64(a²-4)²+(5a²-16)(a²-16)(a²-4)=0
å 为a>c
æ以a²-4>0
æ以64a²-256+5a^4-96a²+256=0
5a^4-32a²=0
a²=32/5
æ以5x²/32+5y²/12=1
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