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a) \(2\frac{1}{4}x-9\frac{1}{4}=20\)
\(\frac{9}{4}x=20+\frac{37}{4}\)
\(\frac{9}{4}x=\frac{80}{4}+\frac{37}{4}\)
\(\frac{9}{4}x=\frac{117}{4}\)
\(x=\frac{117}{4}:\frac{9}{4}\)
\(x=\frac{117}{4}.\frac{4}{9}\)
\(x=13\)
Vậy x=13
a) \(2\frac{1}{4}x-9\frac{1}{4}=20\)
\(\Rightarrow\frac{9}{4}x-\frac{37}{4}=20\)
\(\Rightarrow\frac{9}{4}x=20+\frac{37}{4}\)
\(\Rightarrow\frac{9}{4}x=\frac{117}{4}\)
\(\Rightarrow x=\frac{117}{4}:\frac{9}{4}\)
\(\Rightarrow x=13\)
Vậy x = 13
b) \(0,25x-\frac{1}{5}x=\frac{13}{20}\)
\(\Rightarrow\left(0,25-\frac{1}{5}\right)x=\frac{13}{20}\)
\(\Rightarrow\frac{1}{20}x=\frac{13}{20}\)
\(\Rightarrow x=\frac{13}{20}:\frac{1}{20}\)
\(\Rightarrow x=13\)
Vậy x = 13

a) \(-3+x=-5\)
\(x=-5-\left(-3\right)\)
\(x=-2\)
b) \(\frac{x}{4}=\frac{20}{8}\)
\(8x=80\)
\(x=10\)

1.\(x⋮15v\text{à }0< x\le40\)
\(\Rightarrow x\in B\left(15\right)v\text{à }0< x\le40\)
\(x\in\left\{15;30\right\}\)
2.\(x\in\text{Ư}\left(20\right)v\text{à }x>8\)
\(\Rightarrow x\in\left\{10;20\right\}\)
3.\(16⋮x\)
\(\Rightarrow x\in\text{Ư}\left(16\right)\)
\(x\in\left\{1;2;4;8;16\right\}\)
4.\(x⋮5v\text{à }x< 20\)
\(\Rightarrow x\in B\left(5\right)v\text{à }x< 20\)
\(x\in\left\{0;5;10;15\right\}\)
Bài 2:Bội của 7 là 14;28;35;77

1/3x + 2/5x + 2/5 =0
x(1/3 +2/5)+2/5 =0
x11/15 +2/5 =0
x11/15 =-2/5
x=-6/11

\(\left|a+2\right|=a\)
\(\Rightarrow a+2=\hept{\begin{cases}a\\-a\end{cases}}\)
\(\Rightarrow\hept{\begin{cases}a-a=2\\-a-a=2\end{cases}}\)
\(\Rightarrow\hept{\begin{cases}0=2\left(loai\right)\\-2a=2\end{cases}}\)
\(\Rightarrow a=-1\)
\(\frac{a+4}{20}=\frac{5}{a+4}\)
\(\Rightarrow\left(a+4\right)^2=20\cdot5\)
\(\Rightarrow\left(a+4\right)^2=100\)
\(\Rightarrow\hept{\begin{cases}a+4=10\\a+4=-10\end{cases}}\)
\(\Rightarrow\hept{\begin{cases}a=6\\a=-14\end{cases}}\)

a) \(3x-\frac{1}{5}=\frac{4+x}{2}\)
=> \(\frac{15x-1}{5}=\frac{4+x}{2}\)
=> \(\left(15x-1\right).2=\left(4+x\right).5\)
=> \(30x-2=20+5x\)
=> \(30x-5x=20+2\)
=> \(25x=22\)
=> \(x=\frac{22}{25}\)
b) \(\frac{4}{3}x-1=\frac{4\left(x+1\right)}{3}-\frac{1}{3}\)
=> \(\frac{1}{3}x=\frac{4x+4-1}{3}\)
=> \(\frac{1}{3}x=\frac{4x+3}{3}\)
=> \(3x=3\left(4x+3\right)\)
=> \(3x=12x+9\)
=> \(3x-12x=9\)
=> \(-9x=9\)
=> \(x=9:\left(-9\right)=-1\)