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\(\frac{x}{-5}=\frac{8}{10}\)
\(x=\frac{8}{10}\cdot-5\)
\(x=-4\)
\(\frac{20}{x}=\frac{-6}{30}\)
\(x=20:\frac{-6}{30}\)
\(x=-100\)
\(\frac{25}{-10}=\frac{x}{4}\)
\(x=\frac{25}{-10}\cdot4\)
\(x=-10\)
a) \(x\ge2\Leftrightarrow x-2\ge0\)
\(\Leftrightarrow\left|x-2\right|=x-2\)
\(3\left(x-2\right)+2x=19\)
\(\Leftrightarrow3x-6+2x=19\)
\(\Leftrightarrow5x=25\)
\(\Leftrightarrow x=5\)
b)\(\frac{1}{5}< \frac{x}{30}< \frac{1}{4}\)
\(\Leftrightarrow\frac{12}{60}< \frac{2x}{60}< \frac{15}{60}\)
Do \(x\in N\)nên ta có: \(\hept{\begin{cases}2x\in N\\2x⋮2\\12< 2x< 15\end{cases}}\)
\(\Rightarrow2x=14\)
\(\Leftrightarrow x=7\)
a) <=> 3x-6+2x=19
<=> 5x=25 => x=25:5=5
b) <=> 30/5<x<30/4 <=> 6< x < 7,5
x là số tự nhiên nên x=7
\(\Rightarrow\frac{x+10}{490}+\frac{x+20}{480}+\frac{x+30}{470}+\frac{x+40}{460}+\frac{x+50}{450}+5=0\)
\(\Rightarrow\frac{x+10}{490}+1+\frac{x+20}{480}+1+\frac{x+30}{470}+1+\frac{x+40}{460}+1+\frac{x+50}{450}+1=0\)
\(\Rightarrow\frac{x+500}{490}+\frac{x+500}{480}+\frac{x+500}{470}+\frac{x+500}{460}+\frac{x+500}{450}=0\)
\(\Rightarrow\left(x+500\right).\left(\frac{1}{490}+\frac{1}{480}+\frac{1}{470}+\frac{1}{460}+\frac{1}{450}\right)=0\Rightarrow x+500=0\Rightarrow x=-500\)
15) 70 - 5 . ( x - 3 ) = 45
5 . ( x - 3 ) = 70 - 45
5 . ( x - 3 ) = 25
x - 3 = 25 : 5
x - 3 = 5
x = 5 + 3
x = 8
14 ) x : ( 1001 : 13 ) = 29
x : 77 = 29
x = 29 . 77
x = 2233
13 ) 420 : ( x : 39 ) = 105
x : 39 = 420 : 105
x : 39 = 4
x = 4 . 39
x = 156
\(460+85\) x \(4=\frac{x+175}{5}+30\)
\(460+340=\frac{x+175}{5}+30\)
\(800=\frac{x+175}{5}+30\\ \frac{x+175}{5}=800-30\\ \frac{x+175}{5}=770\)
\(x+175=770\) x \(5\)
\(x+175=3850\\ x=3850-175\\ x=3675\)
460 - 80 x 4 = ( x + 200) : 4
460 - 340 = (x + 200) : 4
120 = ( x + 200) : 4
x + 200 = 120 x 4
x + 200 = 480
x = 480 - 200
x = 280