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â 对äºæç©çº¿y²=2pxï¼è¿ç¦ç¹å¼¦ç´çº¿æ¹ç¨ï¼y=k(x-p/2)ã设ç´çº¿ä¸æç©çº¿äº¤ä¸(x1,y1)ã(x2,y2)两ç¹ï¼åä¸ç¹åæ æ¯ï¼
X = (x1+x2)/2
Y = (y1+y2)/2
â¡ å°y=k(x-p/2)ä»£å ¥y²=2px ï¼
(k(x - p/2))² = 2px
k²(x² -px +p²/4) = 2px
x² -(p -2p/k²)x + p²/4 == 0
x1 + x2 = p(1 + 2/k²)
å° x = (y/k + p/2) ä»£å ¥y²=2px ï¼
y²=2p(y/k + p/2)
y²-2p/k y - p² = 0
y1 + y2 = 2p/k
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X = p(1 + 2/k²)/2=p/2 + p/k²
Y = p/k
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X = p/2 + Y²/p
Y²= p(x - p/2)
ä»£å ¥p=2
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Y² = 2(X -1)
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