ѵ6 ֵ
ֵǽ߿ص֮һ.ҪֵĸַúֵʵӦ.
ѵų
()mʵM={m|m>1},f(x)=log3(x2-4mx+4m2+m+ ).
(1)֤mMʱf(x)ʵ;֮f(x)ʵx壬mM.
(2)mMʱf(x)Сֵ.
(3)֤ÿmM,f(x)СֵС1.
̽
[1]һҪΪ4840 cm2,ĿߵıΪ(<1),ϡ¸8 cmĿհףҸ5 cmհףȷĸߴ磬ʹֽС?Ҫˡ[ ]ôΪֵʱʹֽС?
ͼҪ齨ϵʽСֵ⣬ͬʱѧ֪ʶʵＶĿ.
֪ʶУҪݺżԺСֵȻ֪ʶ.
֤S()[ ]ϵĵ׳βװӦתΪֵ.
뷽Ӧ⣬ؼǽѧģͣתΪֵ.
⣺軭Ϊx cm,Ϊx cm,x2=4840,ֽΪS cm2,S=(x+16)(x+10)=x2+(16+10)x+160,x= ʽãS=5000+44 (8 + ),8 = ,= <1)ʱSȡСֵ.ʱߣx= =88 cm,x= ×88=55 cm.
ˡ[ ] ܦ1<2 ,Sıʽã
,8- >0,
S(1)-S(2)<0,S()[ ]ڵ.
Ӷڦˡ[ ],= ʱS()ȡСֵ.
𣺻Ϊ88 cm,Ϊ55 cmʱֽС.Ҫˡ[ ],= ʱֽС.
[2]֪f(x)= ,x[1,+ (1)a= ʱf(x)Сֵ.
(2)x[1,+ ,f(x)>0ʵaȡֵΧ.
ͼҪ麯СֵԼ⣬ѧۺϷԼＶĿ.
֪ʶУҪͨf(x)ֵaȡֵΧת˼۵˼.
ǰaȡֵΧתΪֵ.
뷽ⷨһת˼f(x)>0תΪxĶβʽ;ⷨ÷˼.
(1)⣺a= ʱf(x)=x+ +2
f(x)[1+ Ϊ
f(x)[1+ ϵСֵΪf(1)= .
(2)ⷨһ[1+ ϣf(x)= >0 x2+2x+a>0.
y=x2+2x+a,x[1,+ y=x2+2x+a=(x+1)2+a-1
൱x=1ʱymin=3+a,ҽymin=3+a>0ʱf(x)>0a>-3.
ⷨf(x)=x+ +2,x[1,+ a0ʱf(x)ֵΪ;
a<0ʱf(x)ʵx=1ʱf(x)min=3+a,
ҽf(x)min=3+a>0ʱf(x)>0a>-3.
ѵ漰⼰ķҪУ
(1)ֵ
Ҫֵij÷䷽ԷͼԪʽ.ʲôֵ뿼ǺĶ.
(2)ۺĿ
Ҫ麯ֵԡżԡһЩ֪ʶϵĿ.
Ҫ߱ϸߵѧ˼άۺϷԼǿ.ڽۺԻΪȵص㣬ǿ.
(3)úֵʵ
ؼǰʵתΪ⣬Ӷѧ֪ʶȥ.Ҫнǿķѧģ.
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