cos6度cos42度 cos66度

1-(sin^6a+cos^6a)根据a^3+b^3=(a+b)(a^2-a*b+b^2)=1-[(sin^2a+cos^2a)*(sin^4a-sin^2acos^2a+cos^4a)]根据sin^

cos43=sin47=0.73sin43=cos47=0.68cot43=tan47=1.07sin45=cos45=1.41tan45=1sin2=sin(47-45)=sin47*cos45-s

（2）y=cosx在（3π/4,π）上单调递减,在（π,6π/5）上单调递增,由y=cosx关于x=π对称,得cos6π/5cos9π/8（4）cos（-5π/6）=cos（-5π/6+2π）=cos

原式=[cos15sin9+sin(15-9)]/[sin15sin9-cos(15-9)]=(cos15sin9+sin15cos9-cos15sin9)/(sin15sin9-cos15cos9-

y=sin^6x+cos^6=(sin^2x+cos^2x)(sin^4x-sin^2xcos^2x+cos^4x)=sin^4x-sin^2xcos^2x+cos^4x=sin^4x+2sin^2x

原式=（sin26°*cos74°+cos42°）/（sin26°*cos74°+cos42°）=1

(1-cos^6α-sin^6α)/(1-cos^4α-sin^4α)1=sin^2α+cos^2α原式=(sin^2α+cos^2α-cos^6α-sin^6α)/(sin^2α+cos^2α-co

代入cos2π/7+cos4π/7+cos6π/7=4cos1π/7cos2π/7cos3π/7-1=-1/2做这样的题和差化积是一定要掌握的.cosA+cosB=2cos(A+B)/2*再问：可不可

a=1/2cos6°-√3/2sin6°=sin30°cos6°-cos30°sin6°=sin(30°-6°)=sin24°b=2tan13°/(1+tan13°)=tan26°cos50°=cos

cos20cos40cos80=sin20cos20cos40cos80/sin20=(1/2)sin40cos40cos80/sin20=(1/4)sin80cos80/sin20=(1/8)sin

因为1-2sin^2θ=cos2θ所以2sin^23θ=1-cos6θ-2sin^2θ=-1+cos3θ原式=2sin^23θ-2sin^2θ=cos2θ-cos6θ把π/10带入2sin²

原式cos6°*cos54°*cos66°=cos6°*cos（60-6）*cos（60+6）=cos6*（cos60*cos6+sin60*sin6）（cos60cos6-sin60*sin6）=c

角度0°30°45°60°90°sin01/2√2/2√3/21cos1√3/2√2/21/20tan0√3/31√3不存在这是最常用的.你的太多了打不下,其他的用公式换算

=√3/2

3045607590sin1/2√2/2√3/2√2/21cos√3/2√2/21/2(√6-√2)/40tan√3/31√3-√3/8-1/2不存在

cos(-60°)=cos60°=1/2sin2π/3=sin(π-2π/3)=sinπ/3=√3/2tan5π/4=tan(5π/4-π)=tanπ/4=1cos11π/6=cos(2π-11π/6

(sin6+cos15*sin9)/(cos6-sin15*sin9)=[sin(15-9)+cos15*sin9]/[cos(15-9)-sin15sin9]=(sin15cos9-cos15sin

等于3/2

原式=[cos15sin9+sin(15-9)]/[sin15sin9-cos(15-9)]=(cos15sin9+sin15cos9-cos15sin9)/(sin15sin9-cos15cos9-

sinx＋sin^2x＝1,sinx=(-1+√5）/2sinx=cos^2xcos^2x＋cos^6x=cos^2x(cos^4x+1)=sinx(sin^2x+1)=sinx(1-cos^2x+1