5、两向量a,b所在直线夹角为 π/4 lt 0, 那么下列说法正确的是 ()-|||-A、a,b夹角 dfrac (pi )(4) B、a,b夹角 dfrac (3pi )(4)-|||-C、a,b夹角可能 dfrac (3pi )(4) 或 dfrac (pi )(4) D.以上都不对

(B) pi +dfrac (4)(3) (C) pi +2 . (D) pi +dfrac (8)(3)

[单选题]设向量a=（-2，4，4），b=（0，6，3），则a与b的夹角为（）．A . B . C . D .

(B) dfrac (lambda )(2pi {varepsilon )_(0)a}. (C) dfrac (lambda )(4pi {varepsilon

(3) (int )_(0)^dfrac (pi {4)}dfrac (x)(1+cos 2x)dx= () .-|||-(A) dfrac (pi )(8)+

dfrac (pi )(3)B . dfrac (pi )(3)C . dfrac (pi )(3)D . dfrac (pi )(3)[单选题]复数1+i对应

(B) dfrac (9)(4pi {varepsilon )_(0)a}-|||-(C) -dfrac (9)(8pi {varepsilon )_(0)a}

(B) .dfrac ({mu )_(0)I}(2pi R)+dfrac (3{mu )_(0)I}(8R)-|||-(c) dfrac ({mu )_(0)I

C-|||-R-|||-+Q-|||-(B) dfrac (qQ)(4pi {varepsilon )_(0)R} , -dfrac (qQ)(4pi {var

3.要使函数φ(x )= ,dfrac {pi )(2)] (B)[π,2π] (C) [ 0,dfrac (pi )(2)] (D) [ dfrac

A dfrac (4)(5);B dfrac (4)(5);C dfrac (4)(5);D dfrac (4)(5).某学生依次进行三门课程的考试,第一门课程