2. 2. 4 Frequency representation of periodic signals In a finite interval of time, a periodic signal x(t)can be represented by its fourier series when it complies with the Dirichlet conditions a (t)=+2(a, cosnoot+ bm, sin noot) (2.12) Where 2c7/2 x(tcos nootdi (213) T/2 b x(tsin n@tdt (214) TJ7/2 n=0,1,2,3, 7= the period Wo= the angular frequency or circular frequency Wo=2TT/T an (including ao and bn)are called Fourier coefficientsIn a finite interval of time, a periodic signal x(t) can be represented by its Fourier series when it complies with the Dirichlet conditions: where n＝0,1,2,3,…… T= the period ω0= the angular frequency or circular frequency ω0= 2π/T an(including a0 and bn ) are called Fourier coefficients. 2.2.4 Frequency representation of periodic signals   = = + + 1 0 0 0 ( cos sin ) 2 ( ) n n n a n t b n t a x t   (2.12) − = / 2 / 2 0 ( ) cos 2 T T n x t n tdt T a  (2.13) − = / 2 / 2 0 ( )sin 2 T T n x t n tdt T b  (2.14)