试证;对任意的正整数n,有1/(1*2*3)+1/(2*3*4)+.+1/n(n+1)(n+2)
来源:学生作业帮 编辑:搜搜考试网作业帮 分类:数学作业 时间:2024/05/15 00:55:44
试证;对任意的正整数n,有1/(1*2*3)+1/(2*3*4)+.+1/n(n+1)(n+2)
1/n(n+1)(n+2)=1/n·[1/(n+1) - 1/(n+2)]=1/n(n+1) - 1/n(n+2) =[1/n-1/(n+1)] - ½[1/n-1-(n+2)]
=½[1/n-2/(n+1)+1/(n+2)].
∴原式=½(1/1-2/2+1/3)+½(1/2-2/3+1/4)+½(1/3-2/4+1/5)+···+½[1/n-2/(n+1)+1/(n+2)]
=½(1/1+1/2+1/3+···+1/n) - 1·[1/2+1/3+1/4+···+1/(n+1)] + ½[1/3+1/4+···+1/(n+2)]
=½[1+1/2+1/(n+1)+1/(n+2)] + 1·[1/3+1/4+···+1/n] - 1·[1/2+1/3+1/4+···+1/(n+1)]
=1/2+1/4 + ½[1/(n+1)+1/(n+2)] - [1/2+1/(n+1)]
=1/4-½[1/(n+1)-1/(n+2)]
=½[1/n-2/(n+1)+1/(n+2)].
∴原式=½(1/1-2/2+1/3)+½(1/2-2/3+1/4)+½(1/3-2/4+1/5)+···+½[1/n-2/(n+1)+1/(n+2)]
=½(1/1+1/2+1/3+···+1/n) - 1·[1/2+1/3+1/4+···+1/(n+1)] + ½[1/3+1/4+···+1/(n+2)]
=½[1+1/2+1/(n+1)+1/(n+2)] + 1·[1/3+1/4+···+1/n] - 1·[1/2+1/3+1/4+···+1/(n+1)]
=1/2+1/4 + ½[1/(n+1)+1/(n+2)] - [1/2+1/(n+1)]
=1/4-½[1/(n+1)-1/(n+2)]
证明对任意正整数n,不等式ln(1/n+1)>1/n^2-1/n^3
证明:对任意的正整数n,有1/1×3+1/2×4+1/3×5+.+1/n(n+2)
证明对任意的正整数n,不等式ln(1/n+1)>1/n^2-1/n^3都成立
对大于1的任意正整数n,都有1+1/2+1/3+1/4+...+1/n>ln(e^n/n!)
证明:对任意的正整数n,不等式2+3/4+4/9+…+(n+1)/n^2>In(n+1)都成立!若bn=(n-2)*(1
证明:对任意正整数n(n+1)(n+2)(n+3)+1都是这个完全平方数
证明对于大于1的任意正整数n都有 In n>1/2+1/3+1/4+...1/n
是否存在大于1的正整数m,使得f(n)=(2n+7)·3^n+9对任意正整数n都能被m整除?
用数学归纳法证明:f(n)=3*5^(2n+1)+2^(3n+1)对任意正整数n,f(n)都能被17整除
对任意正整数n,试说明3^n+1 -2^n+2 +3^n -2^n 一定能被10整除
n为任意正整数,那么1/2n(n+1)-1的值是质数的n有几个
已知函数f(x)=(2^n-1)/(2^n+1),求证:对任意不小于3的自然数n,都有f(n)>n/(n+1)