问题
选择题
cos275°+cos215°+cos75°•cos15°的值是( )
|
答案
cos275°+cos215°+cos75°•cos15°=cos275°+sin275°+sin15°•cos15°
=1+
sin30°=1 2 5 4
故选A.
cos275°+cos215°+cos75°•cos15°的值是( )
|
cos275°+cos215°+cos75°•cos15°=cos275°+sin275°+sin15°•cos15°
=1+
sin30°=1 2 5 4
故选A.