so sánh:
a)\(\frac{201,7x2018+1}{201,8x2019+1}và\frac{201,6x2017+1}{201,7x2018+1}\) b)\(\frac{1}{5}+\frac{1}{6}+\frac{1}{7}+\frac{1}{8}+\frac{1}{9}+\frac{1}{10}+\frac{1}{11}+...+\frac{1}{14}và\frac{3}{2}\)
c)\(\frac{1}{2x2}+\frac{1}{3x3}+\frac{1}{4x4}+...+\frac{1}{2018x2018}và1\)
ta co
1/2.2<1/1*2
...
1/2018*2018<1/2017*2018
=>1/2*2+...+1/2018*1018<1/1*2+...+1/2017.2018
.....(tinh 1/1*2+...+1/2017.*2018)
=>1/2*2+...+1/2018*2018<1-1/2018<1
=>1/2*2+...+1/2018*2018<1