化简(1)sinπ/8cosπ/8 (2)tan81°-cot54°/1+tan81°cot54°(3)sin70°cos25°-sin25°cos70°
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化简(1)sinπ/8cosπ/8 (2)tan81°-cot54°/1+tan81°cot54°(3)sin70°cos25°-sin25°cos70°
化简(1)sinπ/8cosπ/8 (2)tan81°-cot54°/1+tan81°cot54°(3)sin70°cos25°-sin25°cos70°
化简(1)sinπ/8cosπ/8 (2)tan81°-cot54°/1+tan81°cot54°(3)sin70°cos25°-sin25°cos70°
解
sinπ/8cosπ/8
=1/2(2sinπ/8cosπ/8)
=1/2sinπ/4
=√2/4
sin70cos25-sin25cos70
=sin(70-25)
=sin45
=√2/2
tan81-cot54/(1+tan81cot54)
=(tan81-tan36)/(1+tan81tan36)=tan(81-36)=tan45=1
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