Partial fraction得：5/(x+2) - 3/(x+1)= 5/[4+(x-2)] - 3/[3+(x-2)]= (5/4)[1 - (x-2)/4 + ((x-2)/4)^2 - ... + (-1)^n ((x-2)/4)^n]-[1 - (x-2) + (x-2)^2 - ... + (-1)^n (x-2)^n], n from 0 to oo
