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a ) Ta có : 4(x - 5) - 3(x + 7) = -19
<=> 4x - 20 - 3x - 21 = -19
=> x - 41 = -19
=> x = -19 + 41
=> x = 22
b) Ta có " 7(x - 3) - 5(3 - x) = 11x - 5
<=> 7x - 21 - 15 + 5x = 11x - 5
<=> 12x - 36 = 11x - 5
=> 12x - 11x = -5 + 36
=> x = 31
a) \(2\left(x-5\right)-3\left(x+7\right)=14\)
\(\Leftrightarrow2x-10-3x-21=14\)
\(\Leftrightarrow-x-31=14\)
\(\Leftrightarrow-x=45\Leftrightarrow x=-45\)
b) \(5\left(x-6\right)-2\left(x+3\right)=12\)
\(\Leftrightarrow5x-30-2x-6=12\)
\(\Leftrightarrow3x-36=12\)
\(\Leftrightarrow3x=48\Leftrightarrow x=16\)
c) \(3\left(x-4\right)-\left(8-x\right)=12\)
\(\Leftrightarrow3x-12-8+x=12\)
\(\Leftrightarrow4x-20=12\)
\(\Leftrightarrow4x=32\Leftrightarrow x=8\)
d) \(-7\left(3x-5\right)+2\left(7x-14\right)=28\)
\(\Leftrightarrow-21x+35+14x-28=28\)
\(\Leftrightarrow-7x+35=0\Leftrightarrow x=5\)
Bài 1: <Cho là câu a đi>:
a. \(\frac{1}{2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{x\left(x+1\right)}=\frac{49}{50}\)
\(\rightarrow\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{x\left(x+1\right)}=\frac{49}{50}\)
\(\rightarrow1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{x}-\frac{1}{x+1}=\frac{49}{50}\)
\(\rightarrow1-\frac{1}{x+1}=\frac{49}{50}\)
\(\rightarrow\frac{1}{x+1}=1-\frac{49}{50}=\frac{1}{50}\)
\(\rightarrow x+1=50\rightarrow x=49\)
Vậy x = 49.
a.\(\Rightarrow\left(\frac{3}{5}+x\right):\frac{2}{7}=\frac{3}{35}-\frac{2}{7}\)
\(\Rightarrow\left(\frac{3}{5}+x\right):\frac{2}{7}=-\frac{1}{5}\)
\(\Rightarrow\frac{3}{5}+x=-\frac{1}{5}.\frac{2}{7}\)
\(\Rightarrow\frac{3}{5}+x=-\frac{2}{35}\)
\(\Rightarrow x=-\frac{2}{35}-\frac{3}{5}\)
Vậy \(x=-\frac{23}{35}\).
b. => 5x-1=0 hoặc 2x-1/3=0
=> 5x=1 hoặc 2x=1/3
=> x=1/5 hoặc x=1/6
c. \(\Rightarrow\frac{1}{7}:x=\frac{3}{14}-\frac{3}{7}\)
\(\Rightarrow\frac{1}{7}:x=-\frac{3}{14}\)
\(\Rightarrow x=\frac{1}{7}:\left(-\frac{3}{14}\right)\)
Vậy \(x=\frac{-2}{3}\).
a)\(6:\left(\frac{\frac{3}{5}x+3}{20}+9\right)=\frac{3}{5}\)
\(\frac{\frac{3}{5}x+3}{20}+9=6:\frac{3}{5}\)
\(\frac{\frac{3}{5}x+3}{20}+9=6.\frac{5}{3}\)
\(\frac{\frac{3}{5}x+3}{20}+9=10\)
\(\frac{\frac{3}{5}x+3}{20}=10-9\)
\(\left(\frac{3}{5}x+3\right):20=1\)
\(\frac{3}{5}x+3=1.20\)
\(\frac{3}{5}x+3=20\)
\(\frac{3}{5}x=20-3\)
\(\frac{3}{5}x=17\)
\(x=17:\frac{3}{5}\)
\(x=17.\frac{5}{3}\)
\(x=\frac{85}{3}\)
b)l x+3 l = l -9 l
l x+3l=9
\(\orbr{\begin{cases}x+3=9\\x+3=-9\end{cases}\Rightarrow\orbr{\begin{cases}x=9-3\\x=-9-3\end{cases}\Rightarrow}\orbr{\begin{cases}x=6\\x=-12\end{cases}}}\)
1/a) 12 - x= 1-(-5)
12 - x = 6
x= 12-6
x=6
b)| x+4|= 12
x+4 = \(\pm\)12
*x+4=12
x=8
*x+4= -12
x=-16
2/Tìm n
\(n-5⋮n+2\)
=> \(n+2-7⋮n+2\)
mà \(n+2⋮n+2\)
=> 7\(⋮\)n+2
=> n+2 \(\varepsilon\)Ư(7)= {1;-1;7;-7}
| n+2 | 1 | -1 | 7 | -7 |
| n | -1 | -3 | 5 | -9 |
3/a)4.(-5)2 + 2.(-12)
= 2.2.(-5)2 + 2.(-12)
=2[2.25.(-12)]
=2.(-600)
=-1200
\(a.-8:\left(4\dfrac{1}{5}x+\dfrac{3}{10}\right)=4\dfrac{4}{9}\)
\(4\dfrac{1}{5}x+\dfrac{3}{10}=\left(-8\right):4\dfrac{4}{9}\)
\(4\dfrac{1}{5}x+\dfrac{3}{10}=\dfrac{-9}{5}\)
\(4\dfrac{1}{5}x=\dfrac{-9}{5}-\dfrac{3}{10}\)
\(4\dfrac{1}{5}x=\dfrac{-21}{10}\)
\(x=\dfrac{-21}{10}:\dfrac{21}{5}\)
\(x=\dfrac{-1}{2}\)
Vay \(x=\dfrac{-1}{2}\).
\(b.4\dfrac{2}{3}-\left(\dfrac{3}{5}:x\right)=-20\%\)
\(\dfrac{14}{3}-\left(\dfrac{3}{5}:x\right)=\dfrac{-1}{5}\)
\(\dfrac{3}{5}:x=\dfrac{14}{3}-\dfrac{-1}{5}\)
\(\dfrac{3}{5}:x=\dfrac{73}{15}\)
\(x=\dfrac{3}{5}:\dfrac{73}{15}\)
\(x=\dfrac{9}{73}\)
Vay \(x=\dfrac{9}{73}\).
Câu c; d; e tương tự nhé.
14-(7-x+3)=5-[4-(5-3)] 14-(7-x+3)=5-[4-2] 14-(7-x+3)=5-2 14-(7-x+3)=3 7-x+3=14-3 7-x+3=11 7-x=11-3 7-x=8 x=7-8 x=-1 vậy x=-1
14-(7-x+3)=5-[4-(5-3] 14-(7-x+3)=5-[4-2] 14-(7-x+3)=5-2 14-(7-x+3)=3 7-x +3=14-3 7-x+3=11 7-x=11-3 7-x=8 x=7-8 x=-1