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单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,*,15,.2.3整数指数幂(一),正整数指数幂有哪些运算性质?,(1),a,m,a,n,=a,m+n,(a0 m、n,为正整数),(2)(a,m,),n,=a,mn,(a0 m、n,为正整数),(3)(ab),n,=a,n,b,n,(a,b0 m、n,为正整数),(4),a,m,a,n,=a,m-n,(a0 m、n,为正整数且mn),(5)(b0,n是正整数),当a0时,a,0,=1。(0指数幂的运算),(6),a,m,a,n,=a,m-n,(a0 m、n,为整数),a,5,a,3,=a,2,a,3,a,5,=?,分,析,a,3,a,5,=a,3-5,=a,-2,a,3,a,5,=,=,n是正整数时,a,-n,属于分式。并且,(a0),例如:,引入负整数指数幂后,指数的取值范围就扩大到全体整数。,负指数的意义:,一般地,当,n,是正整数时,,这就是说:a,n,(a0)是a,n,的倒数,(1)3,2,=_,3,0,=_,3,-2,=_;,(2)(-3),2,=_,(-3),0,=_,(-3),-2,=_;,(3)b,2,=_,b,0,=_,b,-2,=_(b0).,练,习,a,3,a,-5,=,a,-3,a,-5,=,a,0,a,-5,=,a,-2,a,-8,a,-5,a,m,a,n,=a,m+n,,这条性质对于m,n是任意整数的情形仍然适用。,归,纳,整数指数幂有以下运算性质:,(1),a,m,a,n,=a,m+n,(a0),(2)(a,m,),n,=a,mn,(a0),(3)(ab),n,=a,n,b,n,(a,b0),(4),a,m,a,n,=a,m-n,(a0),(5)(b0),当a0时,a,0,=1。,(6),a,-3,a,-9,=,(a,-3,),2,=,(ab),-3,=,a,-3,a,-5,=,例题:,(a,-1,b,2,),3,;(2)a,-2,b,2,(a,2,b,-2,),-3,跟踪练习:,(1)x,2,y,-3,(x,-1,y),3,;,(2)(2ab,2,c,-3,),-2,(a,-2,b),3,课堂达标测试,基础题:,1.计算:,(a+b),m+1,(a+b),n-1,;(2)(-a,2,b),2,(-a,2,b,3,),3,(-ab,4,),5,(3)(x,3,),2,(x,2,),4,x,0,(4)(-1.8x,4,y,2,z,3,)(-0.2x,2,y,4,z)(-1/3xyz),提高题:,2.已知 ,,求a,51,a,8,的值;,3.计算:x,n+2,x,n-2,(x,2,),3n-3,;,4.已知:10,m,=5,10,n,=4,求10,2m-3n,.,小,结,n是正整数时,a,-n,属于分式。并且,(a0),
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