全周期傅立叶算法利用N点周期采样值x(0)~x(N)计算二次谐波正弦分量幅值a2的计算公式是
A.(2/N)∑x(k)cos(4∏k/N)
B.(2/N)∑x(k)sin(4∏k/N)
C.(4/N)∑x(k)cos(2∏k/N
D.(4/N)∑x(k)sin(2∏k/N)