含有2n＋1项的等差数列，其奇数项和S1与偶数项的和S2之比为？

是不是要给点奖励啊
设首项为a公差为d
S1=(n+1)(a+nd)
S2=n(a+nd)
之比为1+1/n

设原数列首项为a，公差为d，
原数列依次为a，a+d，a+2d，a+3d，.............，a+2nd

奇数项为：a，a+2d，a+4d，.............，a+2nd
奇数项和：S奇 = [a + (a+2nd)](n+1)/2 = (a+nd)(n+1)

偶数项为：a+d，a+3d，a+5d，.............，a+(2n-1)d
偶数项和：S偶 = [(a+d) + (a+2nd-d)]n/2 = (a+nd)n

S奇/S偶 = (n+1)/n