1、√cos^2(4π/3+2π)=√cos^2(4π/3)=√(-1/2)^2=1/2
2、cos(-80)=cos(80)=k,cos(100)=-cos(80)=-k,sin^2(100)=1-cos^2(100)=1-k^2
又因为sin100>0,所以sin(100)=√(1-k^2),所以tan100=sin100/cos100=-√(1-k^2)/k
3、tan(a-7π)=tan(a)=-3/4,由π/2<a<3π/2,所以sin(a)>0>cos(a),可求得:
sin(a)=3/5,cos(a)=-4/5, 所以sin(a)cos(a)=-1/5
4、已知cos(a)+cos(π-a)=0,所以π-a=2a,得a=π/6 ,所以sin(π/6)+sin(π/3)=√3
5、√(1-2sin40cos40)/[cos(40)-√(cos^2 50)]
=√(cos^2 40-2sin40cos40+sin ^2 40)/[cos(40)-cos(50)]
=(cos40-sin40)/[cos(40)-cos(50)]
=(cos40-sin40)/[cos(40)-si(40)]
=1
追问谢谢,么么哒
追答不客气