分类：教育/科学-学习帮助
问题：(1+cos20`)/(2sin20`)
回答：　(1+cos20)/(2sin20)-sin10(1/tan5-tan5) 
= 2cos²10/(4sin10cos10)-2sin5cos5(cos5/sin5-sin5/cos5)
= cos10/(2sin10)-2(cos²5-sin²5)
= cos10/(2sin10)-2cos10
= (cos10-4sin10cos10)/(2sin10)
= (sin80-2sin20)/(2sin10)
= (sin80-sin20-sin20)/(2sin10)
= (2cos50sin30-sin20)/(2sin10)
= (sin40-sin20)/(2sin10)
= 2cos30sin10/(2sin10)
= cos30
= √3/2