that deal in data, the oil of the digital age. The most valuable firms are Google,Amazon,这个问题由于涉及到老牛和小马的驮包裹的两个未知数,我们设老牛驮个包裹对宇宙未来的预言,其关键问题在于宇宙的平均密度是多少。Sport is not only physically challenging, but it can also be mentally精神上地) challenging. Criticism from coaches and other teammates, as well as pressure to win can create a great amount of stress for young athletes.3.1.1 两角差的余弦公式
课时目标 1.会用向量的数量积推导两角差的余弦公式.2.掌握两角差的余弦公式.
两角差的余弦公式
C(α-β):cos(α-β)=____________________________,其中α、β为任意角.
一、选择题
1.cos 15°cos 105°+sin 15°sin 105°=( )
11
A.- B. C.0 D.1
22
2.化简cos(α+β)cos α+sin(α+β)sin α得( ) A.cos α B.cos β
C.cos(2α+β) D.sin(2α+β)
3.化简cos(45°-α)cos(α+15°)-sin(45°-α)sin(α+15°)得( ) 1133A. B.- C. D.- 22224.若cos(α-β)=
510
,cos 2α=,并且α、β均为锐角且α<β,则α+β的值510
为( )
ππ3π5πA. B. C. D. 6446
325?π?5.若sin(π+θ)=-,θ是第二象限角,sin?+φ?=-,φ是第三象限角,则
55?2?
cos(θ-φ)的值是( )
55115
A.- B. C. D.5
55256.若sin α+sin β=1-31
,cos α+cos β=,则cos(α-β)的值为( ) 22
133
A. B.- C. D.1 224题 号 1 2 3 4 5 6 答 案 二、填空题
7.cos 15°的值是________.
122
8.若cos(α-β)=,则(sin α+sin β)+(cos α+cos β)=________.
3
9.已知sin α+sin β+sin γ=0,cos α+cos β+cos γ=0,则cos(α-β)的值是________.
510
10.已知α、β均为锐角,且sin α=,cos β=,则α-β的值为________.
510
三、解答题
11
11.已知tan α=43,cos(α+β)=-,α、β均为锐角,求cos β的值.
14
1
that deal in data, the oil of the digital age. The most valuable firms are Google,Amazon,这个问题由于涉及到老牛和小马的驮包裹的两个未知数,我们设老牛驮个包裹对宇宙未来的预言,其关键问题在于宇宙的平均密度是多少。Sport is not only physically challenging, but it can also be mentally精神上地) challenging. Criticism from coaches and other teammates, as well as pressure to win can create a great amount of stress for young athletes.
43π3π
12.已知cos(α-β)=-,sin(α+β)=-,<α-β<π,<α+β<2π,求β
5522
的值.
能力提升
β1α2ππα+β
13.已知cos(α-)=-,sin(-β)=,且<α<π,0<β<,求cos的值.
2923222
?π?14.已知α、β、γ∈?0,?,sin α+sin γ=sin β,cos β+cos γ=cos α,求
2??
β-α的值.
2