13,
所以cos C =cos[π-(A +B )]=-cos(A +B ) =sin A ·sin B -cos A ·cos B =35×1213-45×513=16
65
,故选A. 2.(2010·烟台中英文学校质检)sin75°cos30°-sin15°sin150°的值为( ) A .1
B.12
C.2
2
D.32
[答案] C
[解析] sin75°cos30°-sin15°sin150°=sin75°cos30°-cos75°sin30°=sin(75°-30°)=sin45°=
2
2
. 3.(2010·吉林省质检)对于函数f (x )=sin x +cos x ,下列命题中正确的是( ) A .∀x ∈R ,f (x )< 2 B .∃x ∈R ,f (x )< 2 C .∀x ∈R ,f (x )> 2
D .∃x ∈R ,f (x )> 2
[答案] B
[解析] ∵f (x )=2sin ⎝⎛⎭
⎫x +π
4≤2, ∴不存在x ∈R 使f (x )>2且存在x ∈R ,使f (x )=2,故A 、C 、D 均错.
4.(文)(2010·北京东城区)在△ABC 中,如果sin A =3sin C ,B =30°,那么角A 等于( ) A .30°
B .45°
C .60°
D .120°
[答案] D
[解析] ∵△ABC 中,B =30°,∴C =150°-A , ∴sin A =3sin(150°-A )=
32cos A +3
2
sin A , ∴tan A =-3,∴A =120°. (理)已知sin α=
55,sin(α-β)=-10
10
,α、β均为锐角,则β等于( )
A.5π
12 B.π3
C.π4
D.π6
[答案] C
[解析] ∵α、β均为锐角,∴-π2<α-β<π
2,
∴cos(α-β)=1-sin 2(α-β)=310
10,
∴sin α=
5
5
,∴cos α=1-⎝⎛
⎭
⎫552=255.
∴sin β=sin[α-(α-β)]
=sin αcos(α-β)-cos αsin(α-β)=22
. ∵0<β<π2,∴β=π
4
,故选C.
5.(文)(2010·广东惠州一中)函数y =sin ⎝⎛⎭⎫π
3-2x +sin2x 的最小正周期是( ) A.π
2
B .π
C .2π
D .4π
[答案] B [解析] y =
32cos2x -1
2
sin2x +sin2x =sin ⎝⎛⎭⎫2x +π3, ∴周期T =π.
(理)函数f (x )=(3sin x -4cos x )·cos x 的最大值为( ) A .5 B.92
C.12
D.52
[答案] C
[解析] f (x )=(3sin x -4cos x )cos x =3sin x cos x -4cos 2x =3
2sin2x -2cos2x -2
=52sin(2x -θ)-2,其中tan θ=43, 所以f (x )的最大值是52-2=1
2
.故选C.
6.(文)(2010·温州中学)已知向量a =(sin75°,-cos75°),b =(-cos15°,sin15°),则|a -b |的值为( )
A .0
B .1 C. 2
D .2
[答案] D
[解析] ∵|a -b |2=(sin75°+cos15°)2+(-cos75°-sin15°)2=2+2sin75°cos15°+2cos75°sin15°=2+2sin90°=4,∴|a -b |=2.
(理)(2010·鞍山一中)已知a =(sin α,1-4cos2α),b =(1,3sin α-2),α∈⎝⎛⎭⎫0,π
2,若a ∥b ,则tan ⎝⎛⎭
⎫α-π
4=( ) A.17
B .-17
C.27
D .-27
[答案] B
[解析] ∵a ∥b ,∴1-4cos2α=sin α(3sin α-2), ∴5sin 2α+2sin α-3=0,
∴sin α=35或sin α=-1,∵α∈⎝⎛⎭⎫0,π2,∴sin α=35, ∴tan α=34,∴tan ⎝⎛⎭⎫α-π4=tan α-11+tan α=-1
7
. 7.(文)(2010·河南许昌调研)已知sin β=35(π
2<β<π),且sin(α+β)=cos α,则tan(α+β)=
( )
A .1
B .2
C .-2
D.825
[答案] C
[解析] ∵sin β=35,π2<β<π,∴cos β=-4
5,
∴sin(α+β)=cos α=cos[(α+β)-β] =cos(α+β)cos β+sin(α+β)sin β =-45cos(α+β)+3
5
sin(α+β),
∴25sin(α+β)=-4
5
cos(α+β),∴tan(α+β)=-2. (理)(2010·杭州模拟)已知sin x -sin y =-23,cos x -cos y =23,且x ,y 为锐角,则tan(x -
y )=( )
A.214
5
B .-2145
C .±2145
D .±51428
[答案] B
[解析] 两式平方相加得:cos(x -y )=5
9,
∵x 、y 为锐角,sin x -sin y <0,∴x 9
,