（接上题）（2）如果它由入射波与反射波叠加而形成，则产生此驻波的入射波和反射波的波函数为 A: $y_{1}=0.005cos(314t-3.14x)，y_{2}=0.005cos(314t+3.14x)；$ B: $y_{1}=0.005cos(314t+3.14x)，y_{2}=0.005cos(314t+3.14x)；$ C: $y_{1}=0.005cos(314t-3.14x)，y_{2}=0.005cos(314t+3.14x\pm \pi)；$ D: $y_{1}=0.005cos(314t+3.14x)，y_{2}=0.005cos(314t-3.14x)；$

低压燃气管中压为（ ） A: 0.005～0.3mpa B: 0.005～0.1mpa C: 0.005～0.7mpa D: 0.005～0.2mpa

【单选题】sin ( α+β ) = A. sinαcosβ-cosαsinβ B. cosαsin β-sin αcos β C. sinαcosβ+cosαsinβ D. cos αcos β-sin α sin β

【单选题】设y=sin(cos(x)),求 结果为:(本题10.0分) A. cos(cos(x))*cos(x)+ sin(cos(x))*sin(x)^2 B. - cos(cos(x))*cos(x) - sin(cos(x))*sin(x)^2 C. - cos(cos(x))*cos(x)^2 - sin(cos(x))*sin(x)^2 D. - cos(cos(x))*cos(x) ^2- sin(cos(x))*sin(x)

cos(x)*cos(x/2)*cos(x/4)*cos(x/8).cos(x/(2^(n-1))

\(设f(x,y,z)=\frac{x\cos y+y\cos z+z\cos x}{1+\cos x+\cos y+\cos z},则df|_{(0,0,0)}=(\,)\)

sin(α-β)cosβ+cos(α-β)sinβ=( ) A: sin(α-2β) B: cos(α-2β) C: sinα D: cosα

【计算题】已知sinα+cosα=1,求:(1)sinαcosα; (2)sin α-cos α; (3)sin α-cos α

已知向量a=(2,2,1),则a的方向余弦为(). A: cosα=2/3,cosβ=2/3,cosγ=1/3 B: cosα=2/5,cosβ=2/5,cosγ=1/5

已知sinα+sinβ+sinγ=0，cosα+cosβ-cosγ=0，则cos(α-β)的值是[    ]