函數(shù)的單調(diào)性與周一、函數(shù)的

4講函數(shù)的單調(diào)性與我們?cè)诔踔醒芯苛艘淮魏瘮?shù)、二次函數(shù)的圖象，研究了yaxb(a0)yax2bxc(a0[1]

yyx22x

的圖象，并觀察說(shuō)出在定義域(,g(xx22x1的圖象在對(duì)稱軸左方的區(qū)間(,1)是下降的，在對(duì)稱軸右方的區(qū)間)g(x)隨自變量x的增大而增大。1：yf(x)(xA，對(duì)于區(qū)間(ab1x1x2(a,b)，x1x2f(x1f(x2yf(x(ab內(nèi)是增函數(shù)（increasingfunction2x1x2(a,b)，x1x2f(x1f(x2yf(x間(ab內(nèi)是減函數(shù)(decreasingfunction)2、yf(xf(xf(x1f(x是增（減）函數(shù)圖象自左到右上升（下降2、圖象的峰（谷）函數(shù)增（減）變減（增）點(diǎn)函數(shù)的極大（?。﹛If(xM（f(xMx0If(x0 value[3]如圖是定義在閉區(qū)間[-5，5]f(xf(x1f(xxx[說(shuō) 1]函數(shù)的單調(diào)性與定義的區(qū)間有關(guān)，它是函數(shù)的局部性質(zhì)[說(shuō)明3]初等函數(shù)均可分段單調(diào)x1f(xx21(x(1,1的單調(diào)性2f(xx22x3f(xx22x3的單調(diào)區(qū)間3．已知函數(shù)fxR上的減函數(shù)，則滿足f

1x1xA． B． C．1,0∪ D．,1∪（1）f(0)1x0f(x1f(xR設(shè)集A(x,y)f(x2fy2f(1)B(xy)f(axy2)1,aR，ABa的取值范圍。5yf(u)(uR是增函數(shù)，u(x)(xR是減函數(shù)，求復(fù)合函f((xR的單二、函數(shù)的定義：yf(x)(xAxAf(xTf(xT0是常數(shù))f(x為周期函數(shù)，T是f(x)的周期說(shuō)明：（1）周期函數(shù)的定義域至少一Tf(xkTf(x的周期f(xxf(xTf(xf(x2Tf(xxf(axf(axa0)f(x是周期為4a的周期函數(shù)。f(x課后練習(xí)f(x)x22xyx(1y612x參考答問(wèn)題3（1）5,5,1,25,1,2,5是增 2 （2）x1x20,1)x1f(x)f(x)

1

1(xx)11 x x x 1 2 2(xx)x2x1(x

1 x x2) x1 (xx)(x1x2

12由x1x2得，x1x2 又x1,x2(0,x1x2(0, x1x21 則(xx)(x1x21) f(x)f f(x在(0,1)問(wèn)題 例 x1,x2(1,1)且x1ax(x21)x(x2a(xx2xx2)(xxf(x)f(x) 1x22x21 2 (x21)(x21 2 (x21)(x212 ax1x2(x2x1)(x2 a(xx)(xx (x21)(x2 (x21)(x2由x1 x2x1x1,x2(1,x20,x20,x21x211212x1x21,x1x21（1）a0(x2x1)(x1x21) (x21)(x2 （2）a0a(x2x1)(x1x21) (x21)(x2 （3）a0a(x2x1)(x1x21) (x21)(x2

f(x1f(x2f(x1)f(x2f(x1)f(x2

f(x在1,1f(x在區(qū)間1,1f(x在1,1x22xf(x)

x g(x)利用圖象求單調(diào)區(qū)間（ xx2x(,1),(0,1)減(1,0),(1,f

x22x2xx

x3或x1<x

(,1),(13)

(1,1),(3,例 而f(5)(0, f(50)f(5)f f(0) x f(x)(0, f(0)f(x)f(于是f(x) f(（2）x1x2Rx1f(x1f(x2f(x1x2x2f(x2f(x1x2f(x2f(x2f(x2)f(x1x2)∵x2R由（1）及題設(shè)f(x2) 又x1 x1x2由（1）f(x1x2f(x2f(x1x21f(xR

f(x1x2)1f(x1)f(x2Ax,yfx2y2f(1)x,yx2y2Bx,yf(axy2)f(0)x,yaxy2∵A∩B

x2y2 axy2x2ax2)2 (1a2x24ax30316a243(1a2) a23 a a3x1x2Rx1∵u(x)在R上的單調(diào)遞減(x1)(x2) 即u1u2又∵yf(u)在R上是增函數(shù)f(u1)f(u2) y1y2則x1x2時(shí)y1y2f((x))在R上單調(diào)遞減6x 0x解：f(x)x 0x

x2k,2k2kx2k0, f(x)f(x2k)x2k 課后練習(xí)22x3x22x

x