数学
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$\tan \alpha \cdot \cos \alpha = \sin \alpha$ ()
- 正确
- 错误
7.[福建2020适应性模拟]已知 tan alpha =2 ,则-|||-dfrac ({sin )^2alpha -(cos )^2alpha +2}(2{
4.已知 sin alpha =-dfrac (3)(5), 且α是第三象限的角,则 cos alpha = __ ,-|||-tan alpha = __ o
例1(1)(2021·全国甲卷)若 alpha in (0,dfrac (pi )(2)), tan2α-|||-=dfrac (cos alpha )(2-s
dfrac (Fx)(sin alpha ) D. dfrac (Fx)(cos alpha )
1.“sin^2 alpha +sin^2 beta =1”是“sin alpha +cos beta =0”的().A. 充分非必要条件B. 必要非充分条件C
[题目]若 sin alpha =dfrac (1)(3), 则 cos 2alpha = ()()-|||-
lim _(xarrow alpha )dfrac (sin x-sin alpha )(x-alpha )..
6.(单选题)(三角函数基础118)已知 sin alpha -3cos alpha =0 且α是第三象限角,则 sin alpha -cos alpha 的
求下列极限: lim _(xarrow alpha )dfrac (sin x-sin alpha )(x-alpha );求下列极限: ;
cos (3pi +alpha )=cos alpha -|||-A 对-|||-B 错