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A/ \(\frac{4}{5}+\frac{1}{5}x=\left(-\frac{1}{28}\right)\)
\(\frac{1}{5}x=\left(-\frac{1}{28}\right)-\frac{4}{5}\)
\(\frac{1}{5}x=\left(-\frac{5}{140}\right)-\frac{112}{140}\)
\(\frac{1}{5}x=-\frac{117}{140}\)
\(x=\left(-\frac{117}{140}\right):\frac{1}{5}\)
\(x=\left(-\frac{117}{28}\right)\)
B/ \(\left(\frac{3x}{7}+1\right):\left(-4\right)=-\frac{1}{28}\)
\(\frac{3x}{7}+1=\left(-\frac{1}{28}\right).\left(-4\right)\)
\(\frac{3x}{7}+1=\frac{1}{7}\)
\(\frac{3x}{7}=\frac{1}{7}-1\)
\(\frac{3x}{7}=\frac{1}{7}-\frac{7}{7}\)
\(\frac{3x}{7}=-\frac{6}{7}\)
\(\Rightarrow3x=\left(-6\right)\)(theo cách l8)
\(\Rightarrow x=\left(-6\right):3=\left(-2\right)\)
a. \(\frac{4}{5}+\frac{1}{5}x=\frac{1}{28}\)
\(\Leftrightarrow\frac{1}{5}x=\frac{1}{28}-\frac{4}{5}\)
\(\Leftrightarrow\frac{1}{5}x=\frac{5}{140}-\frac{112}{140}\)
\(\Leftrightarrow\frac{1}{5}x=\frac{-107}{140}\)
\(\Leftrightarrow x=\frac{-107}{140}\div\frac{1}{5}\)
\(\Leftrightarrow x=\frac{-107}{140}\times5\)
\(\Leftrightarrow x=\frac{-107}{28}=\)
b. \(\left(\frac{3x}{7}+1\right)\div\left(-4\right)=\frac{-1}{28}\)
\(\Leftrightarrow\left(\frac{3x}{7}+\frac{7}{7}\right)=\frac{-1}{28}\times\left(-4\right)\)
\(\Leftrightarrow\frac{3x+1}{7}=\frac{1}{7}\)
\(\Leftrightarrow3x+1=1\)
\(\Leftrightarrow3x=1-1\)
\(\Leftrightarrow3x=0\Leftrightarrow x=0\)
(x + 1) + (x + 4) + (x + 7) + ... + (x + 28) = 155
10x + (1 + 4 + 7 + ... + 28) = 155
10x + (28 + 1).[(28 - 1) : 3 + 1] : 2 = 155
10x + 29.10 : 2 = 155
10x + 29.5 = 155
10x + 145 = 155
10x = 155 - 145
10x = 10
x = 1
( x + 1 ) + ( x + 4 ) + ( x + 7 ) + ... + ( x + 28 ) = 225
= ( x + x + x + ... + x ) + ( 1 + 4 + 7 + ... + 28 ) = 225
x * 10 + 145 = 225
x * 10 = 225 - 145
x * 10 = 80
x = 80 : 10
x = 8
Mk nhanh nhất đó
\(\frac{3x}{7+1}:\left(-4\right)=\frac{-1}{28}\)
\(\frac{3x}{7+1}\)=\(\frac{-1}{28}.\left(-4\right)\)
\(\frac{3x}{7+1}\)=\(\frac{1}{7}\)
\(\frac{3x}{8}\)=\(\frac{1}{7}\)
\(3x\)=\(\frac{8.1}{7}\)=\(\frac{8}{7}\)
\(x\)=\(\frac{8}{7}\): \(3\)
\(x\)=\(\frac{8}{21}\)
1a) \(\frac{x-3}{x+7}=\frac{-5}{-6}\)
=> \(\frac{x-3}{x+7}=\frac{5}{6}\)
=> (x - 3).6 = 5.(x + 7)
=> 6x - 18 = 5x + 35
=> 6x - 5x = 35 + 18
=> x = 53
b) \(\frac{x-7}{x+3}=\frac{4}{3}\)
=> (x - 7). 3 = (x + 3). 4
=> 3x - 21 = 4x + 12
=> 3x - 4x = 12 + 21
=> -x = 33
=> x = -33
c) \(\frac{x-10}{6}=-\frac{5}{18}\)
=> (x - 10) . 18 = -5 . 6
=> 18x - 180 = -30
=> 18x = -30 + 180
=> 18x = 150
=> x = 150 : 18 = 25/3
d) \(\frac{x-2}{4}=\frac{25}{x-2}\)
=> (x - 2)(x - 2) = 25 . 4
=> (x - 2)2 = 100
=> (x - 2)2 = 102
=> \(\orbr{\begin{cases}x-2=10\\x-2=-10\end{cases}}\)
=> \(\orbr{\begin{cases}x=12\\x=-8\end{cases}}\)
e) \(\frac{7}{x}=\frac{x}{28}\)
=> 7 . 28 = x . x
=> 196 = x2
=> x2 = 142
=> \(\orbr{\begin{cases}x=14\\x=-14\end{cases}}\)
f) \(\frac{40+x}{77-x}=\frac{6}{7}\)
=> (40 + x) . 7 = (77 - x).6
=> 280 + 7x = 462 - 6x
=> 280 - 462 = -6x + 7x
=> -182 = x
=> x = -182
