Chapter 3 Fourier series 534 Convergence(收敛) of the fourier series 1. Approximation(近似性) joo en(=x(0)-x(t)-Error EN=k、O)2m=J,、0(M (1)N↑→EN↓N→0EN>0 )=4=1[nx)%冷最小 1111 Chapter 3 Fourier Series §3.4 Convergence（收敛） of the Fourier Series 1. Approximation(近似性) ( ) j k t k N k N N x t a e 0 ˆ   + =− = e (t) x(t) x (t) N = − N ——Error (1) N  EN  ( ) x(t)e dt T a a j k t T k k 0 1 2 ˆ −    = = E e (t) dt N T N 2   = EN最小 N → EN →0 e (t)e (t)dt T  N N    =