. phˆan Fourier, Fourier cosine v`a Fourier sine; T´ıch chˆa . p suy rˆo . ng v´o . i h`am tro . ng dˆo ´ i v´o . i c´ac ph´ep biˆe ´ n dˆo ’ i t´ıch phˆan Fourier cosine, Fourier v`a Fourier sine; . phˆan Fourier sine v`a Fourier cosine. T´ıch chˆa . p suy rˆo . ng c´o h`am tro . ng dˆo ´ i v´o . i c´ac ph´ep biˆe ´ n dˆo ’ i t´ıch phˆan Fourier cosine v`a Fourier sine. T´ıch chˆa . p suy. Fourier cosine v`a Fourier sine . . . . . . . . . . . . . 93 3.2 T´ıch chˆa . p suy rˆo . ng c´o h`am tro . ng dˆo ´ i v´o . i c´ac ph´ep biˆe ´ n dˆo ’ i t´ıch phˆan Fourier cosine, Fourier v`a Fourier