在平面直角坐标系中,把点P(4,5)绕原点旋转90°得到点P1,则点P1的坐标是( )
A:(5,﹣4)
B:(﹣5,4)
C:(5,﹣4)或(﹣5,4)
D:(4,﹣5)或(﹣4,5)
圆心角是60°且半径为2的扇形面积为____ (结果保留π).
_______ I walked into class, the teacher had started teaching already.