求(2cos80-sin70)/cos70
问题描述:
求(2cos80-sin70)/cos70
答
[2cos(90-10)-sin(60+10)]/cos(60+10)
=(2sin10-sin60cos10-cos60sin10)/(cos60sin10-sin60sin10)
=(3/2sin10-√3/2cos10)/(1/2cos10-√3/2sin10)
=-√3