Page 1 of 102015年考研数学二真题与解析
一、选择题 1—8小题.每小题4分,共32分.
1.下列反常积分收敛的是( )
(A ) (B ) (C ) (D
)2?
2ln x dx x +∞?21ln dx x x +∞?2x x dx e +∞?【详解】当且仅当时才收敛,所以(A )是发散的;21p dx x +∞?
1p
>2+∞?(B )是发散的;22212ln (ln )|x dx x x +∞+∞==+∞?
(C )是发散的;221ln ln ln dx x x x
+∞+∞==+∞?事实上,对于(D ),应该选(D ).22213()|x x x dx x e e e
+∞
-+∞-=-+=?2.函数在内( )2
01sin ()lim x t t t f x x →??=+ ???
(,)-∞+∞(A )连续 (B )有可去间断点(C )有跳跃间断点 (D )有无穷间断点
【详解】220010
sin lim sin ()lim ,t x t x t x x t t t f x e e x x →?→??=+==≠ ???函数在处没有定义,而,所以应该选(B ).0x =00
1lim ()lim x x x f x e →→==3.设函数 ,若在处连续,则( )100000cos ,(),(,),x x f x x x αβαβ?>?=>>??≤?
()f x '0x =(A ) (B ) (C ) (D )1αβ->01αβ<-≤2αβ->02
αβ<-≤【详解】当时,,当时,,0x >1111()cos sin f x x
x x x
ααβββαβ---'=+0x <0()f x '=10011000cos (),()lim lim cos x x x x f f x x x αβαβ
++--+→→''===