Why come out this result?
Can anyone explain it? Please see the attached file
orthogonal, and so the coefficients of multiples of sin(nx) on one side must
be the same as those on the other of such an equation (with a few
assumptions about the nature of the T's anyway - such as the T's and
their second derivatives are integrable on [0,pi], and that we are only interested
in their values on [0,pi] or they are odd priodic functions of period 2pi )