问题: 2cos70-cos170-tan160sin70 2
解答:
2cos70-cos170-tan160sin170+2
=2sin20+cos10+tan20sin10+2
=(2sin20cos20+cos10co20+sin20sin10)/cos20 +2
={sin40+cos(10-20)}/cos20 +2
=(sin40 +cos10)/cos20 +2
=(sin40 +sin80)/cos20 +2
=2sin60cos20/cos20 +2
=2+genhao3
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