已知cosalpha=(1)/(2)，则cos(2pi-alpha)的值为

5.若cosalpha=-(1)/(2)且alphain((pi)/(2),pi)，则alpha=(2)/(3)pi。A. 对B. 错

例1(1)(2021·全国甲卷)若 alpha in (0,dfrac (pi )(2)), tan2α-|||-=dfrac (cos alpha )(2-s

7.[福建2020适应性模拟]已知 tan alpha =2 ,则-|||-dfrac ({sin )^2alpha -(cos )^2alpha +2}(2{

[题目]若 sin alpha =dfrac (1)(3), 则 cos 2alpha = ()()-|||-

2.单选题-|||-已知两个简谐振动为 _(1)=4cos (2pi t+(1)^n)cm ,-|||-._(2)=2cos (2pi t-6pi /c)cm

最α, β∈R^n, 则长 (|alpha ,alpha |)^(pi _{1)}^(pi _{1)}^(k_{1)}^theta (alpha ,beta

(sin x)=dfrac (1)({cos )^2x} in (0,dfrac (pi )(2)),则(sin x)=dfrac (1)({cos )^2x}

已知sin（α-β）=(1)/(3)，cosαsinβ=(1)/(6)，则cos（2α+2β）=（ ）A. $\frac{7}{9}$B. $\frac{1}{

已知向量组 alpha_1 = (t, 2, 1)^T, alpha_2 = (2, t, 0)^T, alpha_3 = (1, -1, 1)^T 线性相关，

1 单选 已知两个同方向的简谐振动_(1)=2cos (1001pi t+dfrac (pi )(3)) __， _(1)=2cos (1001pi t+df