计算:sin6分之25π cos3分之25π

＝（1/2）sinπ/6＝（1/2）×（1/2）＝1/4这题是代入sin2α＝2sinαcosα求得的

=-sin(3分之19π)+cos(6分之25π)=-sin(3分之π）+cos(6分之π）=-根号2/3+根号2/3=0

原式=sin(π/6)+cos(π/3)-tan(π/4)=1/2+1/2-1=0

arccos(cos5π/4)=5π/4arctan(tan4π/3)=4π/3arcsin(sin6)=6

cos(a+5π/12)cos(a+π/6)+cos(π/12-a)cos(π/3-a）=sin(π/2-(a+5π/12))cos(a+π/6)+cos(π/12-a)sin(π/2-(π/3-a）

原式=[－sin(a＋5π)]×[sina]－[－tan(3π/2－a]×[－tana]=[sina]×[sina]－[1/tana]×[tana]=sin²a－1=－cos²a

an(π+a)=-1/2所以tana=-1/2sina/cosa=-1/2-2sina=cosa所以sina*cosa

cos(3分之25派)+sin(-6分之23派)=cos(3分之25派-8派)+sin(-6分之23派+4派)=cos(3分之1派)+sin(6分之1派)=1/2+根号3/2

当cosA＝1/3时候,利用cos^2A+sin^2A=1可知,sinA=2根号2/3或者-2根号2/3sin-1,这个-1应该是上标,它就是arcsin从广义的角度讲,即sin－1不看成函数的话,它

=sin(4π+5π/6)+cos(π/3-10π)+tan(3π/4-7π)=sin5π/6+cosπ/3+tan3π/4=1/2+1/2-1=0

cos(π/6)=cos30度=(根号3)/2.sin(π/6)=sin30度=1/2.π,π/2,π/3,π/4...之类的,化为角度再求.

f(x)=(sin^2x+cos^2x)(sin^4x-sin^2x*cos^2x+cos^4x)=sin^4x-sin^2x*cos^2x+cos^4x=(sin^2x+cos^2x)^2-3sin

π/12就是15°cos15°=cos（45°-30°）然后用诱导公式计算就可以算出cos15°然后平方-1/2就好了不用我一一计算了吧!要自己动手计算一下啊要不是考试的时候很作难的!住你学习愉快!

由cos平方a+cosa-1=0cosa=1-cos^a=sin^2a即sin^2a=cosa代入sin平方a+sin6次方a+sin8次方a=cosa+cos^3a+cos^4a将cos^2a=1-

cos6分之π=½√3

=cosα+cos2π/3*cosα-sin2π/3*sinα+cos4π/3*cosα-sin4π/3*sinα=cosα-1/2cosα-（根号3）/2sinα-1/2cosα+（根号3）/2si

tanA=sinA/cosA=2(sinA+cosA)/(sinA-cosA)=(sinA/cosA+1)/(sinA/cosA-1)=(2+1)/(2-1)=3

cos^2θ+cos^2(θ+2π/3)+cos^2(θ-2π/3)=(1+cos2θ)/2+[1+cos(2θ+4π/3)]/2+[1+cos(2θ-4π/3)]/2=3/2+[cos2θ+cos(

sin(25π/6)+cos(25π/3)+tan(-25π/4)=sin(25π/6-4π)+cos(25π/3-8π)+tan(-25π/4+7π)=sin(π/6)+cos(π/3)+tan(3

cos(-25π/12)=cos(1/12π)=cos(15°)=cos（45°-30°）=cos30°cos45°+sin30°sin45°=4分之（根6加根2）