1:COS(-7π/12) =
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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) =
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)
=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) =
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