/sci/ - Science & Math

you guys know those constants An and Bn that are found using An = half sine expansion of f(x) etc...?
how do I find An if u(x,0) = f(x) is 3 different functions?
I tried 3 seperate integrals (3h/L from 0 to L/3), (h from L/3 to 2L/3) and (-3h/L from 2L/3 to L) but I wasnt sure what to do with them after
I added them together but it wasnt the correct answer
pls halp