求 2sin160-cos170-tan160*sin170 的值.
问题描述：
求 2sin160-cos170-tan160*sin170 的值.
答
2sin160-cos170-tan160sin170
=2sin160 - (cos170 - sin160sin170/cos160)
=2sin160 - (cos170cos160-sin170sin160)/cos160 =2sin160 - cos(170-160)/cos160
=2sin20 + cos10/cos20
=(2sin20cos20+cos10)/cos20
=(sin40+sin80)/cos20
= 2sin(120/2)*cos(40/2) / cos20
=2sin60
=根号3