1/2+1/6+1/12+A+1/N(N+1)=2005/2006,那么N等于多少.不然我就要被妈妈..K了哎!forusonly 能不能说详细一点啊,我懂了马上就给你

1/2+1/6+1/12+.+1/n(n+1)(n为自然数）的值为?A：n+2/n+1 B:n/n+1 C:n-1/n+1 D:n-2/n+1 (3a^n+1+6a^n+2-9a^n)/3a^n-1 (6a^n+2 +3a^n+1 -9a^n)/3a^n-1 （4a^2n-6a^n+1+2a^n)/2a^n 因式分解 设a,n∈N*证明a^2n-(-a)^n≥(a+1)×a^n 计算:(3a^n+2+6a^n+1-9^n)÷3a^n-1 a^(n+1)b^n-4a^(n+2)+3ab^n-12a^2因式分解 2^n/n*(n+1) [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 数列a(n)=n (n+1)(n+2)(n+3),求S(n) 证明不等式：(1/n)^n+(2/n)^n+(3/n)^n+.+(n/n)^n a^n+1+a^n-1-2a^n因式分解 a^n+2+a^n+1-a^n因式分解 a^n+2+a^n+1-3a^n因式分解 如果n是正整数,[(8a^n+3)-(6a^n+2)-(5a^n+1)]/(-a)^n 下列几组力中,合力不可能等于0的是 A.3N 4N 6N B.1N 2N 4N C.2N 4N 6N D.5N 5N 1N 求极限,N趋向无穷,n^2 （(a+1/n)^(1/n)-a^(1/n)）n^2 *((a+1/n)^(1/n)-a^(1/n))