Question

1, Cho

A = \(\frac{1}{1.2}+\frac{1}{3.4}+....+\frac{1}{2005.2006}\)

B = \(\frac{1}{1004.2006}+\frac{1}{1005.2005}+\frac{1}{1006.2004}+.......+\frac{1}{2006.1004}\)

Hãy Tính \(\frac{A}{B}\)

Answer 1

A=1−12+13−14+...+12005−12006=(1+12+...+12006)−(1+12+..+11003)=11004+11005+...+12006" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:18.06px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:41.489em; padding:1px 0px; position:relative; white-space:nowrap; width:749.281px; word-spacing:normal; word-wrap:normal" class="MathJax_CHTML mjx-chtml">A=1−12+13−14+...+12005−12006=(1+12+...+12006)−(1+12+..+11003)=11004+11005+...+12006

13010.B=11004+12006+11005+12005+...+11004=11505(11004+11005+...+12006)" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:18.06px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal; word-wrap:normal" class="MathJax_CHTML mjx-chtml">13010.B=11004+12006+11005+12005+...+11004=11505(11004+11005+...+12006)

Suy ra A/B = 1505

Tham khảo nha 

Answer 2

\(A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+.....+\frac{1}{2005.2006}\)

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+....+\frac{1}{2005}-\frac{1}{2006}\)

\(=1-\frac{1}{2006}\)

\(=\frac{2005}{2006}\)