Question

( Dấu chấm như . là nhân nhé ! )

 

A,

    E = 1/3  + 1/6 + 1/10 + ........+ 1/55

B,

F = 2/1.3  +  2/3.5 +  2/5.7 +.........+ 3/13.15

C,

G = 3/1.3 + 3/3.5 + +3/5.7 + ..............+ 1/17.21

Answer 1

\(B=\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+..+\frac{1}{55}\)

\(B=\frac{2}{6}+\frac{2}{12}+\frac{2}{20}+...+\frac{2}{110}\)

\(B=\frac{2}{2.3}+\frac{2}{3.4}+\frac{2}{4.5}+...+\frac{2}{10.11}\)

\(B=2.\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{10}-\frac{1}{11}\right)\)

\(B=2.\left(\frac{1}{2}-\frac{1}{11}\right)=2.\frac{9}{22}=\frac{9}{11}\)

Answer 2

làm cả 3 nhé 

Answer 3

bạn do not ask why làm sai ở bước 4 rồi