(选做题)曲线C的直角坐标方程为x2+y2-2x=0,以原点为极点,x轴的正半轴为极轴建立积坐标系,则曲线C的极坐标方程为( )。
ρ=2cosθ
Soon all the people at the meeting_____ on the discussion of developing the
local education.
A.collected
B.concentrated
C.agreed
D.concerned
理想变压器原线圈1400匝,副线圈700匝并接有电阻R。当变压器工作时原、副线圈中[ ]
A、电流的频率之比2:1
B、功率之比2:1
C、电流之比2:1
D、电压之比2:1