2019中考数学专题复? 二次函数与多边形存在性问? 解析?- 百度文库 ر

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ã

ֱBCĽʽΪy=kx+b1311ã

ã

ֱBCĽʽΪy=2x+1 CDBC

ֱCDһϵΪ ֱCDĽʽΪy=ãc=

+cCã

=1

ֱCDĽʽΪy=

y=x+2y=ã

ã

QΪ ͼο֪CBD=90ڣ QΪ20򣨣

12ͼֱ֪l1l2ΪyһA߶OA=2OB=1

1ֱдABCꣻ

2֪κy=ax2+bx+cͼABCĽʽ

32еߵĶԳϴPʹPBCΪֱΣֱдP꣮

𡿽⣺1֪ãA02B10 ӰãOC=4 C40

2ȽBCʽã

ã

ٽCʽɵãc=2 ԽʽΪy=x2+x+2

3֪BC=41=5ߵĶԳΪx=1.5 ڷP㣬ݵֱεʿ֪ |yP|=BC=2.5

ʣP1.52.5P1.52.5

13֪κy=x2+bx+cͼĶԳֱx=2ҹA03 1bcֵ

2öκͼxĽBCꣻ

3ijһκͼ󾭹ԭO͸öκͼĶMһκͼǷڵPʹáPBCֱΣڣPꣻڣ˵ɣ 𡿽⣺1κy=x2+bx+cͼĶԳֱx=2ҹA03

ã=23=c

ãb=4c=3 b=4c=3

2b=4c=3ãy=x24x+3 y=0ʱx24x+3=0 ãx1=3x2=1 B30C10

𣺶κͼxĽBCֱǣ3010

ǣy=x24x+3 =x221 ǣ21 һκĽʽy=kx+b ѣ0021ã

ã

y=x

Pǣxx

ȡBCеMMΪԲģBMΪ뾶ֱGH GHɹɶã x22+

ãx1=x2=2

GH21 BBFXύֱF x=3y=xãy=

=12

F3

CCEXύֱE ͬE1

Pǣ2131 𣺴ڣPǣ2131

14ͼֱϵxoyУһκ1֪OCABCCꣻ

2xǷڵPʹPABΪΣڣֱдPꣻڣ˵ɣ

ͼxύڵAyύڵB

𡿽⣺1y=2y=0áAǣOA=

x=0

0Bǣ02

OB=2AB=4

ڡAOBУߡAOB=90㣬OCABC AO2=AC?AB