số cần tìm là :
\(\frac{1}{2}+\frac{3}{28}+\frac{2}{8}+\frac{4}{77}+\frac{5}{176}\)
= \(\frac{1935}{2128}\)
\(\frac{1}{2}+\frac{2}{8}+\frac{3}{28}+\frac{4}{77}+\frac{5}{176}=\frac{15}{16}\)
\(\frac{1}{2}+\frac{2}{8}+\frac{3}{28}+\frac{4}{77}+\frac{5}{176}=\frac{15}{16}\)
1/2 +2/8 +3/28 + 4/77+ 5/ 176 = 1/( 1*2)+ 2(2*4)+3/(4*7)+4/(7*11)+5/(11*16) = 1/1 - 1/2 +1/2 -1/4 +1/4 -1/7 +1/7 - 1/11 +1/ 11 -1/ 16 = 1-1/16 =15/16