1/(n+6)(n+7)+1/(n+7)(n+8)+1/(n+8)(n+9)+1/(n+9)(n+10)=

3n²-n=1 求6n³+7n²-5n+2014 1/(n+6)(n+7)+1/(n+7)(n+8)+1/(n+8)(n+9)+1/(n+9)(n+10)= 组合计算题组合计算题 nC(n-3,n)+P(4,n)=4C(3,n+1)求nC（n+6,3n)+C(3n,n+7) C(17-2n)+C(3n 13+n)=? (5y^n)(-2y^n+1)+(6y^n)(-7y^n+1)(-3y^n) ｛n为正整数｝注意：是n+1 M=(N-1)×1+(N-2)×2+(N-3)×4+(N-4)×8+(N-5)×16+(N-6)×32+(N-7)×64.化简后公式M=? [3n(n+1)+n(n+1)(2n+1)]/6+n(n+2)化简 [3n(n+1)+n(n+1)(2n+1)]/6+n(n+2)化简 下列各组的三个点力,可能平衡的有 并且说明理由A.3N 4N 8NB.3N,5N 7NC.1N 2N 4N D.7N 6N 13N 已知888个连续正整数之和:n+(n+1)+(n+2)+(n+3)+(n+4)+(n+5)+(n+6)+(n+7)+···+(n+887)是一个平方数 求n 若3n^2-n=1,求6n^3+7n^2-5n+2003的值 3n平方-n=1,求6n三次方+7n平方-5n+2014的值, 已知3n²-n=1,求6n³+7 n²-5n+2003的值 对于整数n,(n+2)(n+7)-(n-1)(n+4)是6的倍数吗?试说明理由 lim(1/n^2+4/n^2+7/n^2+…+3n-1/n^2) n^(n+1/n)/(n+1/n)^n lim[(4+7+...+3n+1)/(n^2-n)]= 2^n/n*(n+1) 7n+19/2n+1为整数,则n=?(7n+19)/(2n+1)，n≠0