a[2(n+1)-1]-a(2n-1)=a1+[2(n+1)-1-1]d-[a1+(2n-1-1)d]=2d数列的奇数项是以a1为首项,2d为公差的等差数列.a[2(n+1)]-a(2n)=a1+[2(n+1)-1]d -[a1+(2n-1)d]=2d数列的偶数项是以a2为首项,2d为公差的等差数列.数列共2n项,...