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幼苗
共回答了13个问题采纳率:92.3% 举报
(2cos20°-sin10°)/sin80°
=(2cos20°-cos80°)/sin80°
=[cos20°+(cos20°-cos80°)]/sin80°
={cos20°+[cos(50°-30°)-cos(50°+30°)]}
/[sin80°]
={cos20°+[2sin30°sin50°]}/sin80°
={cos20°+sin50°}/sin80°
={cos20°+cos40°}/sin80°
={cos(30°-10°)+cos(30°+10°)}/sin80°
={2cos30°cos10°}/sin80°
={根号3cos10°}/sin80°
={根号3cos10°}/cos10°
=根号3
1年前
6