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DF/BC=AF/ACï¼
DF=4/3(3-X)ï¼
Sç©å½¢CEDF=DE*DF
=-4/3(X^2-3X)
=-4/3(X-3/2)^2+3ï¼
â´Sæ大=3ã
å³å¾ï¼AB=5ï¼
SÎABC=1/2AC*BC=1/2AB*CHï¼
CH=2.4ï¼
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åÎCFGâ½ÎCABå¾ï¼
CK/CH=FG/ABï¼
(2.4-DG)/2.4=X/5ï¼
12-5DG=2.4Xï¼
DG=12/25(5-X)ï¼
Sç©å½¢DEFG=DE*DG
=-12/25(X^2-5X)
=-12/25(X-5/2)^2+3ï¼
â´Sæ大=3ã
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