Mary _____ her mother _____ the problem.
A:tell; off
B:tells; about
C:telling; for
试推断:
若sinπ2+α=cosπ-α,则α的取值范围( )
如图,在坐标系中放置一菱形OABC,已知∠ABC=60°,OA=1.先将菱形OABC沿x轴的正方向无滑动翻转,每次翻转60°,连续翻转2015次,点B的落点依次为B1,B2,B3,…,则B2015的坐标为____ .