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6 tháng 7 2017
\(4\left(\dfrac{3}{4}+x\right)-\dfrac{1}{5}=7x-\dfrac{1}{7}\)
\(\Leftrightarrow3+4x-\dfrac{1}{5}=7x-\dfrac{1}{7}\)
\(\Leftrightarrow4x-7x=\dfrac{1}{5}-3-\dfrac{1}{7}\)
\(\Leftrightarrow-3x=\dfrac{-103}{35}\)
\(\Leftrightarrow x=\dfrac{103}{105}\)
10 tháng 12 2022
a: \(=\dfrac{-12}{7}\left(\dfrac{4}{35}+\dfrac{31}{35}\right)-\dfrac{2}{7}=\dfrac{-12}{7}-\dfrac{2}{7}=-2\)
b: =(-4)+(-4)+...+(-4)
=-4*25=-100
c: \(=157\cdot\left(-37\right)-41\cdot53+37\cdot157+51\cdot53\)
=10*53
=530
PT
5 tháng 8 2017
a) Áp dụng tính chất của dãy tỉ số bằng nhau ta có:
\(\dfrac{x}{4}=\dfrac{y}{3}=\dfrac{z}{9}=\dfrac{x-3y+4z}{4-3.3+4.9}=\dfrac{63}{31}=2\)
\(\Rightarrow x=8\)
\(\Rightarrow y=6\)
\(\Rightarrow z=18\)
b. c. Xem lại đề.
TC
1 tháng 3 2017
a. \(\Rightarrow\left\{\begin{matrix}\dfrac{-10}{15}=\dfrac{x}{-9}\\\dfrac{-10}{15}=\dfrac{-8}{y}\\\dfrac{-10}{15}=\dfrac{z}{-21}\end{matrix}\right.\Leftrightarrow\left\{\begin{matrix}x=6\\y=12\\z=14\end{matrix}\right.\)
b. \(\Rightarrow\left\{\begin{matrix}\dfrac{-7}{6}=\dfrac{x}{18}\\\dfrac{-7}{6}=\dfrac{-98}{y}\\\dfrac{-7}{6}=\dfrac{-14}{z}\end{matrix}\right.\Leftrightarrow\left\{\begin{matrix}x=-21\\y=84\\z=-12\end{matrix}\right.\)
1 tháng 3 2017
a) Ta có: \(\dfrac{-10}{15}=\dfrac{x}{-9}\)
\(\Rightarrow15x=-10.\left(-9\right)\)
\(\Rightarrow15x=90\)
\(\Rightarrow x=6\)
Khi đó: \(\dfrac{6}{-9}=\dfrac{-8}{y}=\dfrac{z}{-21}\)
\(\Rightarrow y=\dfrac{-8\left(-9\right)}{6}=12\)
và \(z=\dfrac{-8\left(-21\right)}{12}\) \(=14\)
Vậy \(\left[{}\begin{matrix}x=6\\y=12\\z=14\end{matrix}\right.\)
b) Lại có: \(\dfrac{-7}{6}=\dfrac{x}{18}\)
\(\Rightarrow6x=-7.18\)
\(\Rightarrow6x=-126\)
\(\Rightarrow x=-21\)
Khi đó \(\dfrac{-21}{18}=\dfrac{-98}{y}=\dfrac{-14}{z}\)
\(\Rightarrow y=\dfrac{-98.18}{-21}=84\)
và \(z=\dfrac{-14.84}{-98}=12\)
Vậy \(\left[{}\begin{matrix}x=-21\\y=84\\z=12\end{matrix}\right.\)
9 tháng 8 2018
a) 100 - 7 . (x - 5) = 58
7. (x - 5) = 100 - 58
7. (x - 5) = 42
x - 5 = 42 : 7
x - 5 = 6
x = 6 + 5
x = 11
b)\(x+\frac{1}{3}=\frac{7}{26}.\frac{13}{6}\)
\(x+\frac{1}{3}=\frac{7}{12}\)
\(x=\frac{7}{12}-\frac{1}{3}\)
\(x=\frac{3}{12}=\frac{1}{4}\)
30 tháng 7 2018
\(b,\dfrac{1}{5}:x=\dfrac{1}{5}-\dfrac{1}{7}\)
\(\dfrac{1}{5}:x=\dfrac{7}{35}-\dfrac{5}{35}\)
\(\dfrac{1}{5}:x=\dfrac{2}{35}\)
\(x=\dfrac{1}{5}:\dfrac{2}{35}\)
\(x=\dfrac{1}{5}.\dfrac{35}{2}\)
\(x=\dfrac{7}{2}\)
TH
24 tháng 6 2018
a/ 7x - 3x = 3,2 ; b/ \(\dfrac{2}{3}x-\dfrac{1}{2}x=\dfrac{5}{12}\)
x ( 7 - 3 ) = 3,2 ; x ( \(\dfrac{2}{3}-\dfrac{1}{2}\) ) = \(\dfrac{5}{12}\)
x. 4 = 3,2 ; x ( \(\dfrac{4}{6}-\dfrac{3}{6}\) ) = \(\dfrac{5}{12}\)
x = 3,2 : 4 ; x \(\dfrac{1}{6}=\dfrac{5}{12}\)
x = 0,8 ; x = \(\dfrac{5}{12}:\dfrac{1}{6}=\dfrac{5}{12}.6\)
x = \(\dfrac{5}{2}\)
c/\(2\dfrac{1}{4}.\left(x-7\dfrac{1}{3}\right)=1,5\)
\(\dfrac{9}{4}\left(x-\dfrac{22}{3}\right)=\dfrac{3}{2}\)
\(x-\dfrac{22}{3}=\dfrac{3}{2}:\dfrac{9}{4}=\dfrac{3}{2}.\dfrac{4}{9}\)
\(x-\dfrac{22}{3}=\dfrac{2}{3}\)
\(x=\dfrac{2}{3}+\dfrac{22}{3}\)
\(x=\dfrac{24}{3}=8\)
d/\(\left(1-\dfrac{3}{10}-x\right):\left(\dfrac{19}{10}-1-\dfrac{2}{5}\right)+\dfrac{4}{5}=1\)
\(\left(\dfrac{10}{10}-\dfrac{3}{10}-x\right):\left(\dfrac{19}{10}-\dfrac{10}{10}-\dfrac{4}{10}\right)+\dfrac{4}{5}=1\)
\(\left(\dfrac{7}{10}-x\right):\dfrac{5}{10}+\dfrac{4}{5}=1\)
\(\left(\dfrac{7}{10}-x\right):\dfrac{1}{2}=1-\dfrac{4}{5}\)
\(\left(\dfrac{7}{10}-x\right).2=\dfrac{1}{5}\)
\(\dfrac{7}{10}-x=\dfrac{1}{5}:2=\dfrac{1}{5}.\dfrac{1}{2}=\dfrac{1}{10}\)
\(x=\dfrac{7}{10}-\dfrac{1}{10}\)
\(x=\dfrac{6}{10}=\dfrac{3}{5}\)
Chúc bạn học tốt!!!
24 tháng 3 2018
Ta có:\(A=\dfrac{2}{3}\cdot\dfrac{4}{5}\cdot\dfrac{6}{7}\cdot...\cdot\dfrac{98}{99}\)
\(A< \dfrac{3}{4}\cdot\dfrac{5}{6}\cdot\dfrac{7}{8}\cdot...\cdot\dfrac{99}{100}\)
\(\Rightarrow A^2< \dfrac{2}{3}\cdot\dfrac{3}{4}\cdot\dfrac{4}{5}\cdot\dfrac{5}{6}\cdot\dfrac{6}{7}\cdot\dfrac{7}{8}\cdot...\cdot\dfrac{98}{99}\cdot\dfrac{99}{100}\)
\(A^2< \dfrac{2}{100}=\dfrac{1}{50}\)
Mà \(\dfrac{1}{50}< \dfrac{1}{49}\)
\(\Rightarrow A^2< \dfrac{1}{49}\)
\(\Rightarrow A< \dfrac{1}{7}\left(đpcm\right)\)
\(7x=\dfrac{7^{100}}{7^{98}}\\ \Leftrightarrow7x=7^{100-98}=7^2=7.7\\ \Rightarrow x=7\)
Đs....