an = a1+(n-1)d共10项,其中奇数项的和是25/2a1+a3+a5+...+a9 =25/25a1+20d =25/22a1+8d = 5 (1)偶数项和是25a2+a4+...+a10=255a1+25d =25a1+5d =5...谢谢你，我早就算出来了