1:COS(-7π/12) = 2:tan165/(1-tan^215) = 第二题题目打错了,应该是这个:tan165/(1-tan^2 15) =
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![1:COS(-7π/12) = 2:tan165/(1-tan^215) = 第二题题目打错了,应该是这个:tan165/(1-tan^2 15) =](/uploads/image/z/2566879-7-9.jpg?t=1%EF%BC%9ACOS%28-7%CF%80%2F12%29+%3D+2%EF%BC%9Atan165%2F%281-tan%5E215%29+%3D+%E7%AC%AC%E4%BA%8C%E9%A2%98%E9%A2%98%E7%9B%AE%E6%89%93%E9%94%99%E4%BA%86%EF%BC%8C%E5%BA%94%E8%AF%A5%E6%98%AF%E8%BF%99%E4%B8%AA%EF%BC%9Atan165%2F%281-tan%5E2+15%29+%3D)
1:COS(-7π/12) = 2:tan165/(1-tan^215) = 第二题题目打错了,应该是这个:tan165/(1-tan^2 15) =
1:COS(-7π/12) =
2:tan165/(1-tan^215) =
第二题题目打错了,应该是这个:tan165/(1-tan^2 15) =
1:COS(-7π/12) = 2:tan165/(1-tan^215) = 第二题题目打错了,应该是这个:tan165/(1-tan^2 15) =
【参考答案】
1、cos(-7π/12)
=cos(7π/12)
=cos(45°+60°)
=cos45°cos60°-sin45°sin60°
=(√2/2)×(1/2)-(√2/2)×(√3/2)
=(√2-√6)/4
2、tan165°/(1- tan²15°)
=tan(180°-15°)/(1-tan²15°)
=-tan15°/(1-tan²15°)
=(-1/2)×[2tan15°/(1-tan²15°)]
=(-1/2)×tan30°
=(-1/2)×(√3/3)
=-√3/6
1、cos(-7π/12) =cos7π/12=cos(π-5π/12)=-cos5π/12=-cos(π/4+π/3)=-(根号6-根号2)/4
2、 tan165/(1-tan^215)=-tan15/(1-tan^215)=-(2-根号3)/[1-(2-根号3)^2]=(1-根号3)/8
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这个&#是加还是什么啊 47 12是47度12分么?
1.cos(-7π/12) =cos(-π/3-π/4)=cos(-π/3)cos(-π/4)-sin(-π/3)sin(-π/4)=(√2-√6)/4
2.tan165/(1-tan^2 15),其中tan165=tan(180-15°)=-tan15°=√3-2
1-tan^2 15=1-(7-4√3)=4√3-6,那么tan165/(1-tan^2 15)=(√3-2)/(4√3-6)=-√3/6
、cos(-7π/12) =cos7π/12=cos(π-5π/12)=-cos5π/12=-cos(π/4+π/3)=-(根号6-根号2)/4
2、 tan165/(1-tan^215)=-tan15/(1-tan^215)=-(2-根号3)/[1-(2-根号3)^2]=(1-根号3)/8