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函數(shù),二、積分上限函數(shù)及其導(dǎo)數(shù) 4 a b xyo定理1 如果 )( xf 在 ],[ ba 上連續(xù),則積分上限的函數(shù)dttfxxa??? )()( 在 ],[ ba 上具有導(dǎo)數(shù),且它的導(dǎo)數(shù)是 )()()( xfdttfdxdxxa??? ? ? )( bxa ?? . 積分上限函數(shù)的性質(zhì) xx ??證 dttfxx xxa??????? )()()()( xxx ????????dttfdttf xaxxa ?? ?? ?? )()()(x?x5 ?dttfdttfdttf xaxxxxa ??? ??? ? )()()( ?,)(? ?? xxx dttf?由積分中值定理得 xf ???? )(? ],[ xxx ????,0 xx ?? ??),(???? fx ? ).(limlim00 ?????? fx xx ?? ?).()( xfx ???a b xyo xx ??)(x?x6 、變限積分求導(dǎo)公式2)())(()1( xfdttfxa ???)())(())(()2( )( xuxufdttfxua ????)())(())(()3( )( xvxvfdttfb xv ?????)())(()())(())(()4( )( )( xvxvfxuxufdttfxu xv ??????)( 2證明 ))(())(( )()( dttfdxddttf xuaxua ?? ??dxxdudttfxdud xua)())(()()( ?? ?).())(( xuxuf ??7 25( ) s i n , ( )xF x t d t F x?? ? 求例 1解 2( ) s i n ( ) ( )F x x x??? 1s i n2x x??例2 sin 4( ) 2 , ( ) .xxF x t d t F x???? 求4( ) 2 s i n ( s i n )F x x x??? ? ?42 x??解 ? s in .2 xx44c o s 2 s i n 2 .x x x? ? ? ?8 例 3 求 2c o s120l i m .x txe d tx???解 2c o s1x td e d tdx ??因2c o s ( c o s )xex? ??? 2c o ss i n ,xxe ?? ? ?2c o s120limx txe d tx??? 2c o s0s i nlim 2 xxxex ?????1 1 .22e e?? ? ? ?所以由洛必塔法則 9 例 4 設(shè) )( xf 在 ),( ???? 內(nèi)連續(xù) , 且 0)( ?xf . 證明函數(shù)???xxdttfdtttfxF