![](https://rs.olm.vn/images/avt/0.png?1311)
Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
`(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`
![](https://rs.olm.vn/images/avt/0.png?1311)
TA có
4-2/2*4+6-4/4*6+8-6/6*8+...+2016-2014/2014*2016
=1/2-1/4+1/4-1/6+...+1/2014-1/2016
=1/2+1/4-1/4+1/6-1/6+...+1/2014-1/2014-1/2016
=1/2-1/2016
=1007/2016
![](https://rs.olm.vn/images/avt/0.png?1311)
2[1/2X4+1/4X6+1/6X8+...+1/Xx(X+2)]=11/45x2
2/2x4+2/4x6+2/6x8+....+2/Xx(X+2)=22/45
1/2-1/4+1/4-1/6+1/6-1/8+...+1/x-1/x+2=22/45
1/2-1/x+2=22/45
1/x+2=1/2-22/45
1/x+2=1/90
=>x+2=90
=>x=88
vậy x=88
\(\frac{1}{2.4}+\frac{1}{4.6}+\frac{1}{6.8}+...+\frac{1}{x\left(x+2\right)}=\frac{11}{45}\)
\(\Rightarrow\frac{2}{2.4}+\frac{2}{4.6}+\frac{2}{6.8}+...+\frac{2}{x\left(x+2\right)}=\frac{22}{45}\)
\(\Rightarrow\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+\frac{1}{6}-\frac{1}{8}+...+\frac{1}{x}-\frac{1}{x+2}=\frac{22}{45}\)
\(\Rightarrow\frac{1}{2}-\frac{1}{x+2}=\frac{22}{45}\)
\(\Rightarrow\frac{1}{x+2}=\frac{1}{2}-\frac{22}{45}\)
\(\Rightarrow\frac{1}{x+2}=\frac{1}{90}\)
=>x+2=90
=>x=90-2
=>x=88
vậy x=88
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{1}{2.4}+\frac{1}{4.6}+\frac{1}{6.8}+...+\frac{1}{98.100}\)
\(=\frac{1}{2}\left(\frac{2}{2.4}+\frac{2}{4.6}+\frac{2}{6.8}+....+\frac{2}{98.100}\right)\)
\(=\frac{1}{2}\left(\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+....+\frac{1}{98}-\frac{1}{100}\right)\)
\(=\frac{1}{2}\left(\frac{1}{2}-\frac{1}{100}\right)=\frac{49}{200}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(=\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+\frac{1}{6}-\frac{1}{8}+\frac{1}{8}-\frac{1}{10}+\frac{1}{10}-\frac{1}{12}+\frac{1}{12}-\frac{1}{14}+\frac{1}{14}\)
\(=\frac{1}{2}-\frac{1}{14}\)
\(=\frac{3}{7}\)
\(\frac{2}{2\times4}+\frac{2}{4\times6}+\frac{2}{6\times8}+\frac{2}{8\times10}+\frac{2}{10\times12}+\frac{2}{12\times14}\)
\(=\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+\frac{1}{6}-\frac{1}{8}+\frac{1}{8}+\frac{1}{10}-\frac{1}{10}+\frac{1}{12}-\frac{1}{14}+\frac{1}{14}\)
\(=\frac{1}{2}-\frac{1}{14}\)
\(=\frac{7}{14}-\frac{1}{14}\)
\(=\frac{6}{14}=\frac{3}{7}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Để giải phương trình \( y:(\frac{1}{2} \times 4+\frac{1}{4} \times 6+\frac{1}{6} \times 8+\frac{1}{8} \times 10) \times y=\frac{1}{3} \), ta có thể làm như sau:
Đầu tiên, tính giá trị của phần tử ngoặc đơn trong phương trình:
\( \frac{1}{2} \times 4+\frac{1}{4} \times 6+\frac{1}{6} \times 8+\frac{1}{8} \times 10 \).
\( = \frac{2}{2} \times 4+\frac{1}{2} \times 6+\frac{1}{3} \times 8+\frac{1}{4} \times 10 \).
\( = 2+3+\frac{8}{3}+\frac{10}{4} \).
\( = 2+3+\frac{8}{3}+2.5 \).
\( = 5+2.667+2.5 \).
\( = 10.167 \).
Tiếp theo, thay giá trị tính được vào phương trình:
\( y \times 10.167 = \frac{1}{3} \).
Để tìm giá trị của y, ta chia cả hai vế của phương trình cho 10.167:
\( y = \frac{\frac{1}{3}}{10.167} \).
Tiếp tục tính toán:
\( y = \frac{1}{3} \times \frac{1}{10.167} \).
\( y \approx 0.030 \).
Vậy giá trị của y là khoảng 0.030.
[1/(2 × 4) + 1/(4 × 6) + 1/(6 × 8) + 1/(8 × 10)] × y = 1/3
(1/2 - 1/4 + 1/4 - 1/6 + 1/6 - 1/8 + 1/8 - 1/10) × y = 1/3
(1/2 - 1/10) × y = 1/3
2/5 × y = 1/3
y = 1/3 : 2/5
y = 5/6
![](https://rs.olm.vn/images/avt/0.png?1311)
\(a,\frac{4}{2.4}+\frac{4}{4.6}+\frac{4}{6.8}+....+\frac{4}{16.18}+\frac{4}{18.20}\)
\(=\frac{4}{2}\left(\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+\frac{1}{6}-\frac{1}{8}+...+\frac{1}{18}-\frac{1}{20}\right)\)
\(=2\left(\frac{1}{2}-\frac{1}{20}\right)\)
\(=2.\frac{9}{20}\)
\(=\frac{9}{10}\)
\(b,\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+...+\frac{1}{90}\)
\(=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{9.10}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}\)
\(=1-\frac{1}{10}\)
\(=\frac{9}{10}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{2}{2\times4}+\frac{2}{4\times6}+\frac{2}{6\times8}+\frac{2}{8\times10}\)
\(=\frac{2}{2}-\frac{2}{4}+\frac{2}{4}-\frac{2}{6}+\frac{2}{6}-\frac{2}{8}+\frac{2}{8}-\frac{2}{10}\)
\(=\frac{2}{2}-\frac{2}{10}\)
\(=1-\frac{1}{5}\)
\(=\frac{4}{5}\)
A=\(\frac{2}{2x4}+\frac{2}{4x6}+.........+\frac{2}{2014x2016}\)
=\(\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+.............+\frac{1}{2014}-\frac{1}{2016}\)
=\(\frac{1}{2}-\frac{1}{2016}\)
=\(\frac{1008}{2016}-\frac{1}{2016}\)
=\(\frac{1007}{2016}\)
mình nghĩ nguyễn hung phat làm đúng sồi