两个同方向同频率简写振动方程分别为 $ x_1 = 0.6\cos(2t + \frac{5}{6}\pi) $ 和 $ x_2 = 0.8\cos(2t - \frac{1}{6}\pi) $ （SI制），则合振动方程为（ ）
1. $ x = 0.1\cos(2t + \frac{1}{3}\pi) $
2. $ x = 0.2\cos(2t + \frac{1}{6}\pi) $
3. $ x = 0.2\cos(2t - \frac{1}{6}\pi) $
4. $ x = 0.1\cos(2t + \frac{1}{6}\pi) $
设 M=int_(-(pi)/(2))^(pi)/(2) (sin x)/(1+x^2) cos^4 x dx，N=int_(-(pi)/(2))^(pi)/(
设曲线 ) x=(cos )^2t y=(sin )^2t z=sin tcos t .设曲线上对应于点处法平面方程为（ ）
[单选题]一平面简谐波的波动方程为y=0.1cos（3πt-πx+-π）（SI），t=0时的波形曲线如图所示，则下列叙述中哪个正确？（）A . O点的振幅为-0.1mB . 频率γ=3HzC . 波长为2mD . 波速为9m/s
(int )_(-dfrac {pi )(2)}^dfrac (pi {2)}((cos )^2x+dfrac (xcos x)(1+{cos )^2x})dx
(d)/(dx)int_(sin x)^cos x cos(pi t^2) , dt = ( ). $\frac{d}{dx}\int_{\sin x}^{\c
(sin x)=dfrac (1)({cos )^2x} in (0,dfrac (pi )(2)),则(sin x)=dfrac (1)({cos )^2x}
(int )_(-dfrac {pi )(2)}^dfrac (pi {2)}dfrac (|x|sin x)(1+{cos )^3x}dx=(int )_(-
(15)int_(-(pi)/(2))^(pi)/(2)sqrt(cos x-cos^3)xdx;(15)$\int_{-\frac{\pi}{2}}^{\fr
(int )_(0)^dfrac (pi {4)}dfrac (x)(1+cos 2x)dx=( ) .(int )_(0)^dfrac (pi {4)}dfr
2.求下列函数的极值:-|||-(6) (x)=sin x+cos x(-dfrac (pi )(2)leqslant xleqslant dfrac (pi