2/3×1+2/3×5+2/5×7…2/19×21

2/1*3+2/3*5+2/5*7+……+2/2003*2005 1/1 -1/3 2/3 -3/3 -2/5 3/5 -4/5 5/5 -1/7 2/7 -3/7 …… 求 98个是多少 2/3×1+2/3×5+2/5×7…2/19×21 求和Sn=1^2+3^2+5^2+7^2+…+(2n-1)^2 1+3+5+7+9+……+(2n-1) 等比数列求和：1/2,3/2^2,5/2^3,7/2^4,……,(2n-1)/2^n, 1+3/2+5/2^2 +7/2^3 +…+21/2^10 1.1/1*2+1/2*3+1/3*4+……+1/99*100 2.2/1*3+2/3*5+2/5*7+……+2/97*99 1+2+3+4+5+6+7……+105 1/3 × 2/5+1/5 2/7+1/7 2/9+……1/99 × 2/101 1-2^2-3^2+4^2+5^2-6^2-7^2+……+24^2 求和:1-3×2+5×2^2-7×2^3+……+(2n+1)×(-2)^n 2/1*3+2/3*5+2/5*7……+2/97*99+2/99*101要清楚的~ 1/2+3/2^2+5/2^3+7/2^4+…+2n-1/2^n 1×2×3+2×3×4+3×4×5……+7×8×9 简算? 数学题（急需）1/3^2+1/5^2+1/7^2+……+1/(2n+1)^2=? 计算1+3+5+7…+（2n+1） 3×5/2+5×7/2+7×9/2+……+99×101/2 简便运算