(1)y=-x^2+bx+c æç¹AåCåæ 代å
¥ å¾0=-1-b+c å 4=c ç±æ¤å¾c=4 b=3 æ以y=-x^2+3x+4
(2)y=-x^2+3x+4 å y=x+1 æ¶å»y å¾ x^2-2x-3=0 x1=-1 x2=3 ç¹D为(3,4)
AD^2=(3-(-1))^2+ (4-0)^2=32 AD=4#2 (ç¨#代æ¿â )
设ç¹P(m,n) ç¹På°ç´çº¿y=x+1çè·ç¦»ä¸ºd=|m-n+1|/#2=|m-(-m^2+3m+4)+1|/#2
=|m^2-2m-3|/#2=|(m-1)^2-4|/#2
è¦Sæ大ï¼åªédæ大ï¼å½m=1æ¶ï¼dçæ大å¼=4/#2 æ以Sçæ大å¼=1/2*4#2*4/#2=8
(3)Må¨ADä¸ï¼ç´çº¿ADæ¹ç¨y=x+1
ç´çº¿ACæ¹ç¨x/(-1)+y/4=1 å³4x-y+4=0ï¼1ï¼
ACçä¸ç¹G(-1/2,2) ï¼ è¿Gä¸åç´äºACçç´çº¿ä¸ºy-2=-1/4(x-(-1/2)) ï¼2ï¼
ç±ï¼1ï¼ï¼2ï¼å¾M(-1/2,2)
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