(1)当AB边通过坐标原点O时,求AB的长以及三角形ABC的面积。(2)当角ABC=90度,且斜边AC的长最大时,求AB所在的直线方程。
设ç´çº¿ABçæ¹ç¨ä¸ºï¼y=x+m
ä»£å ¥æ¤åæ¹ç¨ï¼x^2+3y^2=4
å¾ï¼x^2+3(x+m)^2=4
æ´çï¼å¾ï¼4x^2+6mx+3m^2-4-0
ç±â³>0å¾ï¼-4/â3<m<4/â3
x1+x2=-3m/2,x1x2=(3m^2-4)/4
|AB|=â2|x1-x2|=â(8-3m^2/2)
å 为â ABC=90°ï¼Cå¨ç´çº¿Lï¼ABâl
æ以|BC|çé¿å°±æ¯ç´çº¿ABä¸ç´çº¿Lçè·ç¦»
æ |BC|=|m-2|/â2
âµ|AC|^2=|AB|^2+|BC|^2
=8-3m^2/2+(m-2)^2/2
=-m^2-2m+10
=-(m+1)^2+11
â´å½m=-1æ¶ï¼æè¾¹ACçé¿æ大.
â´å½æè¾¹ACçé¿æ大æ¶ï¼ABæå¨ç´çº¿çæ¹ç¨ä¸ºx-y-1=0
ä»£å ¥æ¤åæ¹ç¨ï¼x^2+3y^2=4
å¾ï¼x^2+3(x+m)^2=4
æ´çï¼å¾ï¼4x^2+6mx+3m^2-4-0
ç±â³>0å¾ï¼-4/â3<m<4/â3
x1+x2=-3m/2,x1x2=(3m^2-4)/4
|AB|=â2|x1-x2|=â(8-3m^2/2)
å 为â ABC=90°ï¼Cå¨ç´çº¿Lï¼ABâl
æ以|BC|çé¿å°±æ¯ç´çº¿ABä¸ç´çº¿Lçè·ç¦»
æ |BC|=|m-2|/â2
âµ|AC|^2=|AB|^2+|BC|^2
=8-3m^2/2+(m-2)^2/2
=-m^2-2m+10
=-(m+1)^2+11
â´å½m=-1æ¶ï¼æè¾¹ACçé¿æ大.
â´å½æè¾¹ACçé¿æ大æ¶ï¼ABæå¨ç´çº¿çæ¹ç¨ä¸ºx-y-1=0
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