5/1.4 + 5/4.7 + 5/7.10 + ..... + 5/22.25
= 5/3 . ( 5/1.4 + 5/4.7 + 5/7.10 + ..... + 5/22.25 )
= 5/3 . ( 1/1 - 1/4 + 1/4 - 1/5 + 1/5 - ....... + 1/22 - 1/25 + 1/25 )
= 5/3 . ( 1/1 - 1/25 )
= 5/3 . 24/25
= 8/5
chắc thế bạn ạ
Đặt A=(đa thức trên)
Có A=5(1/1.4+1/4.7+...+1/22.25)
=> A=5/3.(1-1/4+1/4-1/7+1/7-...+1/22-1/25)
=> A=5/3.(1-1/25)
=> A= 5/3.24/25
=> A= 8/5
\(\frac{5}{1.4}+\frac{5}{4.7}+...+\frac{5}{22.25}\)
\(=\frac{5}{3}.\left(\frac{3}{1.4}+\frac{3}{4.7}+....+\frac{3}{22.25}\right)\)
\(=\frac{5}{3}.\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+....+\frac{1}{22}-\frac{1}{25}\right)\)
\(=\frac{5}{3}.\left(1-\frac{1}{25}\right)\)
\(=\frac{5}{3}.\frac{24}{25}=\frac{5.24}{3.25}=\frac{1.8}{1.5}=\frac{8}{5}\)
\(\frac{5}{1.4}+\frac{5}{4.7}+\frac{5}{7.10}+...+\frac{5}{22.25}.\)
\(=\frac{5}{3}.\left(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{22.25}\right)\)
\(=\frac{5}{3}.\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+....+\frac{1}{22}-\frac{1}{25}\right)\)
\(=\frac{5}{3}.\left(1-\frac{1}{25}\right)\)
\(=\frac{5}{3}.\frac{24}{25}=\frac{8}{5}\)
5/1.4 + 5/4.7 + 5/7.10 + .... + 5/22.25 =
= 5. ( 1/1.4 + 1/4.7 + 1/7.10 + ... + 1/22.25 )
= 5/3. ( 1 - 1/4 + 1/4 -1/7 + 1/7 -1/10 + ....+1/22 - 1/25 )
= 5/3 . ( 1 - 1/25 )
= 5/3. 24/25
= 8/5
HOk tốt!!!!!!!!
