FOURIER SERIES
12.21 cn=[(−1)nsinhπ]/[π(1 +n^2 )].Having setx= 0, separate out then=0term
and note that (−1)n=(−1)−n.
12.23 (π^2 −8)/ 16.
12.25 (b) Allanandαnare zero;bn=2(−1)n+1/(nπ)andβn=4/(nπ). You will need
the result quoted in exercise 12.19.