-1,2,-3,4,-5,6,.第奇数项为+n,偶数项为-n,第十个数是“10” 1,4,9,16,25,36……第n项为n²,第十项为10²＝100..0,3,8,15,24,35...…第n项为n²-1,第十项为10²-1＝99三个数的和是10+100+99＝209解...