19.设α，β，γ是向量a的三个方向角，则sin^2alpha+sin^2beta+sin^2gamma=____.

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向量 alpha = ((1)/(2) ), beta = ((3)/(2) ), 向量 gamma 满足 2gamma + alpha = 3beta, 那么

设三阶矩阵 =(alpha ,gamma 1,(y)_(2)), =(beta ,gamma 1,(gamma )_(2))其中 =(alpha ,gamma

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

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设((sin )^2x)=dfrac (x)(sin x)，求((sin )^2x)=dfrac (x)(sin x) .设，求.

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设=(x)^2sin x，则=(x)^2sin xA.正确B.错误设，则A.正确B.错误