化简(1)sinπ/8cosπ/8 (2)tan81°-cot54°/1+tan81°cot54°(3)sin70°cos25°-sin25°cos70°

问题描述:

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=√2/4sin70cos25-sin25cos70=sin(70-25)=sin45=√2/2tan81-cot54/(1+tan81cot54)=(tan81-tan36)/(1+tan81tan36)=tan(81-36)=tan45=1