Chứng minh rằng\(\frac{1}{2^3}+\frac{1}{3^3}+....+\frac{1}{2017^3}< \frac{1}{2^2}\)
A=\(\frac{\frac{1}{2018}+\frac{2}{2017}+\frac{3}{2016}+....+\frac{2017}{2}+\frac{2018}{1}}{\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+....+\frac{1}{2019}}\). Chứng minh rằng A là số nguyên
Mong mọi người giúp
\(A=\frac{1}{2017}+\frac{2}{2017^2}+\frac{3}{2017^3}+...+\frac{2017}{2017^{2017}}+\frac{2018}{2017^{2018}}\). Chứng minh rằng : A < \(\frac{2017}{2016^2}\)
Chứng minh rằng
\(\frac{1}{12}< \frac{1}{2^3}+\frac{1}{3^3}+...+\frac{1}{n^3}+\frac{1}{2017^3}< \frac{508}{2018}\)
(với mọi n>1)
Chứng minh A là một số nguyên dương :
A = \(1+\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2017}+\left(1+\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2017}\right)^2+\)\(\left(\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2017}\right)^2+...+\left(\frac{1}{2017}\right)^2\)
\(\text{Chứng minh rằng:}2017< \sqrt{\frac{2}{1}}+\sqrt[3]{\frac{3}{2}}+\sqrt[4]{\frac{4}{3}}+...+\sqrt[2018]{\frac{2018}{2017}}< 2018\)
Chứng minh rằng \(\sqrt{1+\frac{1}{1^2}+\frac{1}{2^2}}+\sqrt{1+\frac{1}{2^2}+\frac{1}{3^2}}+...+\sqrt{1+\frac{1}{2017^2}+\frac{1}{2018^2}}< 2018\)
Chứng tỏ rằng: \(\frac{1}{3}+\frac{1}{3^2}+\frac{1}{3^3}+...+\frac{1}{3^{2017}}< \frac{1}{2}\)
Ta có: \(A=\frac{1}{3}+\frac{1}{3^2}+\frac{1}{3^3}+...+\frac{1}{3^{2017}}\)
\(3A=1+\frac{1}{3}+\frac{1}{3^2}+...+\frac{1}{3^{2016}}\)
\(2A=3A-A=1-\frac{1}{3^{2017}}\)
=> \(A=\left(1-\frac{1}{3^{2017}}\right):2\)
\(A=\frac{1}{2}-\frac{1}{3^{2017}}:2< \frac{1}{2}\)
Vậy: \(A< \frac{1}{2}\)
Chứng minh rằng: 1+ \(\frac{1}{1!}\)+\(\frac{1}{2!}\)+\(\frac{1}{3!}\)+...+\(\frac{1}{2017!}\)<3
Xét \(A=\frac{1}{1!}+\frac{1}{2!}+\frac{1}{3!}+...+\frac{1}{2017!}\)
\(A=1+1-\frac{1}{2!}+\frac{1}{2!}-\frac{1}{3!}+...+\frac{1}{2016!}-\frac{1}{2017!}=2-\frac{1}{2017!}< 2\)
Như vậy A+1<2+1=3
Vậy ta có đpcm
cho S =\(1+\frac{1}{2^2}+\frac{1}{3^2}+...+\frac{1}{2017^2}\)
chứng minh rằng S lớn hơn 2
Trừ 1 đi thì ta chỉ cần chứng minh từ \(\frac{1}{2^2}+\frac{1}{3^2}+...+\frac{1}{2017^2}\) \(\frac{1}{2^2}< \frac{1}{1.2}=\frac{1}{1}-\frac{1}{2}\) \(\frac{1}{3^2}< \frac{1}{2.3}=\frac{1}{2}-\frac{1}{3}\) ....... cứ nhu vậy cho đến \(\frac{1}{100^2}< \frac{1}{99.100}=\frac{1}{99}-\frac{1}{100}\)
Vì \(\frac{1}{2^2}+\frac{1}{3^2}+...+\frac{1}{100^2}< 1-\frac{1}{100}=\frac{99}{100}< 1\)
Vậy S < 2