1.已知sin=,则cos(π-2α)=( A )
A. B.-
C. D.-
2.已知函数f(x)=asin(πx+α)+bcos(πx+β),且f(4)=3,则f(2 018)的值为( C )
A.-1 B.1
C.3 D.-3
解析:∵f(4)=asin(4π+α)+bcos(4π+β)=asin α+bcos β=3,
∴f(2 018)=asin(2 018π+α)+bcos(2 018π+β)=asin α+bcos β=3.故选C.
3.已知sin α-cos α=,α∈(0,π),则sin 2α=( A )
A.-1 B.-
C. D.1
4.设a=sin 33°,b=cos 55°,c=tan 35°,则( C )
A.a>b>c B.b>c>a
C.c>b>a D.c>a>b
解析:由诱导公式可得b=cos 55°=cos (90°-35°)=sin 35°,
由正弦函数的单调性可知b>a,
而c=tan 35°=>sin 35°=b,
∴c>b>a.故选C.
5.若=,则tan θ=( D )
A.1 B.-1
C.3 D.-3
6.(2018·石家庄模拟)已知α为锐角,且2tan(π-α)-3cos+5=0,tan(π+α)+6