12函數f(t)=2cos(3t),0≤t≤ ，若在 t = 0 處，f (t)的傅立葉餘弦級數（Fourier cosine series）收斂到 A，傅立葉正弦級數（Fourier sine series）收斂到 B；在 t =處，f(t)的傅立葉餘弦級數（Fourier cosine series）收斂到 C，傅立葉正弦級數（Fourier sine series）收斂到 D。則 A,B,C,D 各值為何？ (A) A = 0, B = 0, C = 0, D = 0 (B) A = 2, B = 0, C = -2, D = 0 (C) A = 0, B = 2, C = -2, D = 0 (D) A = 2, B = 0, C = 2, D = 0