VC
0
K
Khách
Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
Các câu hỏi dưới đây có thể giống với câu hỏi trên
15 tháng 5 2022
1: =>x:7/3=-3/2
hay \(x=-\dfrac{3}{2}\cdot\dfrac{7}{3}=-\dfrac{7}{2}\)
2: \(x=\dfrac{11}{15}:\dfrac{2}{5}=\dfrac{11}{15}\cdot\dfrac{5}{2}=\dfrac{55}{30}=\dfrac{11}{6}\)
3: \(x=-\dfrac{6}{5}:\dfrac{3}{10}=\dfrac{-6}{5}\cdot\dfrac{10}{3}=\dfrac{-60}{15}=-4\)
4: \(x=\dfrac{1}{3}+\dfrac{3}{20}=\dfrac{20+9}{60}=\dfrac{29}{60}\)
6: \(\Leftrightarrow x\cdot\dfrac{13}{20}=\dfrac{5}{4}\)
hay \(x=\dfrac{5}{4}:\dfrac{13}{20}=\dfrac{5}{4}\cdot\dfrac{20}{13}=\dfrac{100}{52}=\dfrac{25}{13}\)
NT
3
MV
8 tháng 8 2017
\(\dfrac{2x}{15}+\dfrac{2x}{35}+\dfrac{2x}{63}+...+\dfrac{2x}{195}=\dfrac{4}{5}\\ x\cdot\left(\dfrac{2}{15}+\dfrac{2}{35}+\dfrac{2}{63}+...+\dfrac{2}{195}\right)=\dfrac{4}{5}\\ x\cdot\left(\dfrac{2}{3\cdot5}+\dfrac{2}{5\cdot7}+\dfrac{2}{7\cdot9}+...+\dfrac{2}{13\cdot15}\right)=\dfrac{4}{5}\\ x\cdot\left(\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+...+\dfrac{1}{13}-\dfrac{1}{15}\right)=\dfrac{4}{5}\\ x\cdot\left(\dfrac{1}{3}-\dfrac{1}{15}\right)=\dfrac{4}{5}\\ x\cdot\dfrac{4}{15}=\dfrac{4}{5}\\ x=\dfrac{4}{5}:\dfrac{4}{15}\\ x=3\)
Gọi \(D=\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{8}-\dfrac{1}{16}+\dfrac{1}{32}-\dfrac{1}{64}\)
\(2D=1-\dfrac{1}{2}+\dfrac{1}{4}-\dfrac{1}{8}+\dfrac{1}{16}-\dfrac{1}{32}\\ 2D+D=\left(1-\dfrac{1}{2}+\dfrac{1}{4}-\dfrac{1}{8}+\dfrac{1}{16}-\dfrac{1}{32}\right)+\left(\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{8}-\dfrac{1}{16}+\dfrac{1}{32}-\dfrac{1}{64}\right)\\ 3D=1-\dfrac{1}{2}+\dfrac{1}{4}-\dfrac{1}{8}+\dfrac{1}{16}-\dfrac{1}{32}+\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{8}-\dfrac{1}{16}+\dfrac{1}{32}-\dfrac{1}{64}\\ 3D=1-\dfrac{1}{64}< 1\\ \Rightarrow D=\dfrac{1-\dfrac{1}{64}}{3}< \dfrac{1}{3}\)
Vậy \(\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{8}-\dfrac{1}{16}+\dfrac{1}{32}-\dfrac{1}{64}< \dfrac{1}{3}\)
NT
1
S
15 tháng 4 2019
\(\frac{3x}{5}=\frac{1}{3}+\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}+\frac{1}{143}\)
Ta có: \(\frac{1}{3}+\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}+\frac{1}{143}\)
\(=\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+\frac{1}{9.11}+\frac{1}{11.13}\)
\(=\frac{1}{2}.\left(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}+\frac{2}{11.13}\right)\)
\(=\frac{1}{2}.\left(\frac{1}{1}-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}\right)\)
\(=\frac{1}{2}.\left(1-\frac{1}{13}\right)\)
\(=\frac{1}{2}.\frac{12}{13}\)
\(=\frac{6}{13}\)
\(\frac{3x}{5}=\frac{6}{13}\)
\(\Rightarrow3x=\frac{6.5}{13}\)
\(\Rightarrow3x=\frac{30}{13}\)
\(\Rightarrow x=\frac{10}{13}\)
~Học tốt~
DQ
3
3 tháng 4 2016
\(M=\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+...+\frac{1}{49.51}\)
\(M=\frac{1}{2}\left(1-\frac{1}{51}\right)\)
M=\(\frac{1}{2}.\frac{50}{51}=\frac{25}{51}\)
3 tháng 4 2016
\(M=\frac{1}{3}+\frac{1}{15}+\frac{1}{35}+...+\frac{1}{2499}\)
\(M=\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+...+\frac{1}{49.51}\)
\(M=\frac{1}{2}.\left(\frac{1}{1}-\frac{1}{3}+...+\frac{1}{49}-\frac{1}{51}\right)\)
\(M=\frac{1}{2}.\left(\frac{1}{1}-\frac{1}{51}\right)\)
\(M=\frac{1}{2}.\frac{50}{51}\)
\(M=\frac{25}{51}\)
AM
12 tháng 6 2015
a)\(A=\frac{1}{15}+\frac{1}{35}+...+\frac{1}{195}=\frac{1}{3.5}+\frac{1}{5.7}+...+\frac{1}{13.15}=\frac{1}{2}\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{13}-\frac{1}{15}\right)=\frac{1}{2}\left(\frac{1}{3}-\frac{1}{15}\right)=\frac{2}{15}\)
b)\(M=1+3+3^2+...+3^{25}=\frac{3^{26}-1}{3-1}=\frac{3^{26}-1}{2}<\frac{3^{26}}{2}\Rightarrow M
KN
22 tháng 7 2015
a) => (35:x+3)*15 = 165-15=150
=> 35:x+3 = 150:15=10
=> 35:x = 10-3 = 7
=> x = 35:7 = 5
b) => 1*3/10x :1/2 +4/5 =1
=> 1*3/10x:1/2 =1-4/5=1/5
=> 1*3/10x = 1/5 *1/2 =1/10
=> 3/10-x = 1/10
=> x = 3/10 - 1/10 = 2/10 = 1/5