函數(shù)y=f(x)(x∈R)有下列命題:
(1)在同一坐標(biāo)系中,y=f(x-1)與y=f(-x+1)的圖象關(guān)于直線x=-1對(duì)稱;
(2)若f(2-x)=f(x),則函數(shù)y=f(x)的圖象關(guān)于直線x=1對(duì)稱;
(3)若f(x-1)=f(x+1),則函數(shù)y=f(x)是周期函數(shù),且2是一個(gè)周期;
(4)若f(2-x)=-f(x),則函數(shù)y=f(x)的圖象關(guān)于(1,0)對(duì)稱.其中正確命題的序號(hào)是______.
解:根據(jù)題意,依次分析4個(gè)命題:
對(duì)于(1):y=f(x)的圖象與y=f(-x)的圖象關(guān)于y軸對(duì)稱,將y=f(x)向右平移一個(gè)單位得到f(x-1)的圖象,
將y=f(-x)的圖象向右平移一個(gè)單位得到y(tǒng)=[-(x-1)]=f(-x+1)的圖象,則在同一坐標(biāo)系中,y=f(x-1)與y=f(-x+1)的圖象關(guān)于直線x=1對(duì)稱,則(1)錯(cuò)誤;
對(duì)于(2):在f(2-x)=f(x)中,令t=x-1,則f(1-t)=f(1+t),分析可得函數(shù)y=f(x)的圖象關(guān)于直線x=1對(duì)稱,則(2)正確;
對(duì)于(3):在f(x-1)=f(x+1)中,令t=x-1,有f(t)=f(t+2),則函數(shù)y=f(x)是周期函數(shù),且2是一個(gè)周期,(3)正確;
對(duì)于(4):在f(2-x)=-f(x)中,令t=x-1,則f(1-t)=-f(1+t),則函數(shù)y=f(x)的圖象關(guān)于(1,0)對(duì)稱,則(4)正確;
綜合可得,正確命題的序號(hào)是(2)、(3)、(4),
故答案為(2)、(3)、(4).
分析:根據(jù)題意,依次分析4個(gè)命題:對(duì)于(1):y=f(x)的圖象與y=f(-x)的圖象關(guān)于y軸對(duì)稱,由圖象變化的規(guī)律分析如何由將y=f(x)得到f(x-1)的圖象,如何由y=f(-x)得到y(tǒng)=[-(x-1)]=f(-x+1)的圖象,進(jìn)而判斷可得(1)錯(cuò)誤;對(duì)于(2):在f(2-x)=f(x)中,用換元法,令t=x-1,可得f(1-t)=f(1+t),分析可得(2)正確;對(duì)于(3):在f(x-1)=f(x+1)中,令t=x-1,有f(t)=f(t+2),由周期函數(shù)的定義,分析可得(3)正確;對(duì)于(4):在f(2-x)=-f(x)中,用換元法,令t=x-1,則f(1-t)=-f(1+t),分析可得,則(4)正確;綜合可得答案.
點(diǎn)評(píng):本題考查抽象函數(shù)及其應(yīng)用,涉及抽象函數(shù)的對(duì)稱問(wèn)題,關(guān)鍵掌握函數(shù)關(guān)于直線、點(diǎn)對(duì)稱的規(guī)律與判斷方法.