Question

[Moon_Kutea]

TÍNH NHANH:

         C =      1      +      1      +      1      +      1      +      1      +      1     

                    2             14             35            65           104          152

Answer 1

[Lung Thị Linh]

\(C=\frac{1}{2}+\frac{1}{14}+\frac{1}{35}+\frac{1}{65}+\frac{1}{104}+\frac{1}{152}\)

\(\Leftrightarrow C=\frac{2}{4}+\frac{2}{28}+\frac{2}{70}+\frac{2}{130}+\frac{2}{208}+\frac{2}{304}\)

\(\Leftrightarrow C=\frac{2}{1.4}+\frac{2}{4.7}+\frac{2}{7.10}+\frac{2}{10.13}+\frac{2}{13.16}+\frac{2}{16.19}\)

\(\Leftrightarrow\frac{3}{2}C=\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+\frac{3}{13.16}\)

\(\Leftrightarrow\frac{3}{2}C=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+\frac{1}{13}-\frac{1}{16}+\frac{1}{16}\)

\(\Leftrightarrow\frac{3}{2}C=1-\frac{1}{16}\)

\(\Leftrightarrow\frac{3}{2}C=\frac{15}{16}\)

\(\Leftrightarrow C=\frac{5}{8}\)

Answer 2

[Karry Joy]

Ta có

     C =1/2 +1/14 +1/35 +1/65 +1/104 +1/152

=>C. 3/2= 3/4+ 3/4.7 +3/7.10 +3/10.13 +3/13.16 + 3/16.19

=>C. 3/2= 3/4+ 1/4-1/7 +1/7 -1/10 + 1/10-1/13 +1/13 -1/16  +1/16 -1/19

=>C.3/2=1- 1/19 =18/19 =>C = 12/19