分类：教育/科学-学习帮助
问题：2sin160
回答：要用到很差化积，你学了没？2sin160-cos170-tan160sin170=2sin(180-20)-cos(180-10)-tan(180-20)sin(180-10)=2sin20 + cos10 + tan20sin10=2sin20 + cos10 + (sin20/cos20)sin10=2sin20 + [cos10 + (sin20sin10)/cos20]=2sin20 + [cos10cos20 + sin20sin10]/cos20=2sin20 + cos(20-10)/cos20=2sin20 + cos10/cos20=(2sin20cos20 + cos10)/cos20=(sin40 + cos10)/cos20=(cos50 + cos10)/cos20=2cos[(50+10)/2]cos[(50-10)/2]/cos20=2cos30cos20/cos20=2cos30=2(√3/2)=√3