`(2/(2xx4)+2/(4xx6)+2/(6xx8)+2/(8xx10))xxy=1/3`

`=>(1/2-1/4+1/4-1/6+1/6-1/8+1/8-1/10)xxy=1/3`

`=>(1/2-1/10)xxy=1/3`

`=>(5/10-1/10)xxy=1/3`

`=>4/10xxy=1/3`

`=>2/5xxy=1/3`

`=>y=1/3:2/5`

`=>y=1/3xx5/2`

`=>y=5/6`

\(\left(\frac{1}{2.4}+\frac{1}{4.6}+\frac{1}{6.8}+\frac{1}{8.10}\right).y=\frac{1}{3}\)

\(\frac{1}{2}\left(\frac{2}{2.4}+\frac{2}{4.6}+\frac{2}{6.8}+\frac{2}{8.10}\right).y=\frac{1}{3}\)

\(\left(\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+\frac{1}{6}-\frac{1}{8}+\frac{1}{8}-\frac{1}{10}\right).y=\frac{1}{3}:\frac{1}{2}=\frac{2}{3}\)

\(\left(\frac{1}{2}-\frac{1}{10}\right).y=\frac{2}{3}\)

\(\frac{2}{5}.y=\frac{2}{3}\)

=> \(y=\frac{2}{3}:\frac{2}{5}\)

=>\(y=\frac{3}{5}\)

sao ra 1phan 3

sao ra 1/2

co ai ko

cuu voi

là 73/36

hu hu co ai ko

\(S=\frac{1}{1.3}-\frac{1}{2.4}+\frac{1}{3.5}-\frac{1}{4.6}+\frac{1}{5.7}-\frac{1}{6.8}+\frac{1}{7.9}-\frac{1}{8.10}\)

\(\Rightarrow S=\frac{1}{2}\left(1-\frac{1}{3}-\frac{1}{2}+\frac{1}{4}+\frac{1}{3}-\frac{1}{5}-\frac{1}{4}+\frac{1}{6}+\frac{1}{5}-\frac{1}{7}-\frac{1}{6}+\frac{1}{8}+\frac{1}{7}-\frac{1}{9}-\frac{1}{8}+\frac{1}{10}\right)\)

\(\Rightarrow S=\frac{1}{2}\left(1+\frac{1}{10}\right)\)

\(\Rightarrow S=\frac{1}{2}.\frac{11}{10}\)

\(\Rightarrow S=\frac{11}{20}\)

ko bao giờ 323445465

=1/2-1/4+1/4-1/6+1/61/8+1/81/10+1/10-1/12

=1/2-1/12

5/12

tk nha

Đặt : \(A=\frac{1}{2.4}+\frac{1}{4.6}+\frac{1}{6.8}+\frac{1}{8.10}+\frac{1}{10.12}\)

\(\Rightarrow2A=\frac{2}{2.4}+\frac{2}{4.6}+\frac{2}{6.8}+\frac{2}{8.10}+\frac{2}{10.12}\)

\(\Rightarrow2A=\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+......+\frac{1}{10}-\frac{1}{12}\)

\(\Rightarrow2A-A=\frac{1}{2}-\frac{1}{12}\)

\(\Rightarrow A=\frac{5}{12}\)

bài duoi giải sai nha

Dặt biểu thức trên là A

ta có\(2A=\frac{2}{2.4}+\frac{2}{4.6}+\frac{2}{6.8}+\frac{2}{8.10}+\frac{2}{10.12}\)

\(2A=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+...+\frac{1}{10}-\frac{1}{12}\)

\(2A=1-\frac{1}{12}=\frac{11}{12}\)

\(A=\frac{11}{12}\)/ 2=\(\frac{11}{24}\)

E=2.(2+2)+4.(2+4)+6.(6+2)+....+98.(98+2).

E=2.2+2.2+2.4+4.4+...+98.98+2.98

E=2.(2+4+6+...+98)+(2.2+4.4+6.6+...+98.98)

E=2.2450+40425.4

E=4900+161700

E=166600

Dấu chấm bằng dấu nhân.

Bạn đúng cho mình đi mình giải thích tại sao :(2.2+4.4+…+98.98)=40425.4

rảnh hả cha nội, người ta hỏi y chứ có hỏi e đâu mà trả lời!

tại sao 2²+4²+6²+...+98²