In geometry, which unit is defined as being equal to the angle subtended at the centre of a circle by an arc equal in length to the radius ?
in geometry, which unit is defined as being equal to the angle subtended at the centre of a circle by an arc equal in length to the radius 
FreebaseQA-train-1174.P0
angle
angle
m.0mwc
measurement_unit.dimension.si_base_unit
m.06h39
radian