- 2sin160
- 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