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3\(x\) - 28 = \(x\) + 36
3\(x\) - \(x\) = 36 + 28
2\(x\) = 64
\(x\) = 64 : 2
\(x\) = 32
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(-45:5.\left(-3-2x\right)=3\)
\(-9.\left(-3-2x\right)=3\)
\(-3-2x=\left(3:-9\right)\)
\(-3-2x=\dfrac{-1}{3}\)
\(-2x=-3-\dfrac{1}{3}\)
-2x=\(\dfrac{-10}{3}\)
\(x=\dfrac{-10}{3}:-2\)
\(x=\dfrac{5}{3}\)
b)
3x - 28 = x + 36
<=> 3x - x = 36 + 28
<=> 2x = 64
<=> x = 32
Vậy x = 32
c)
(-12)2.x = 56 + 10.13.x
144.x = 56 + 130.x
144x – 130 x = 56
14x = 56
x = 56: 14
x = 4
Vậy x = 4
![](https://rs.olm.vn/images/avt/0.png?1311)
a.
\(10-2\left(4-3x\right)=-4\)
\(\Leftrightarrow2\left(4-3x\right)=10+4\)
\(\Leftrightarrow2\left(4-3x\right)=14\)
\(\Leftrightarrow4-3x=7\)
\(\Leftrightarrow3x=-3\)
\(\Leftrightarrow x=-1\)
b.
\(-12+3\left(-x+7\right)=-18\)
\(\Leftrightarrow3\left(-x+7\right)=-18+12=-6\)
\(\Leftrightarrow-x+7=-6:3=-2\)
\(\Leftrightarrow x=9\)
c.
\(-45:5.\left(-3-2x\right)=3\)
\(\Leftrightarrow-9.\left(-3-2x\right)=3\)
\(\Leftrightarrow-3-2x=-\dfrac{1}{3}\)
\(\Leftrightarrow2x=-\dfrac{8}{3}\)
\(\Leftrightarrow x=-\dfrac{4}{3}\notin Z\left(loại\right)\)
Câu này em ghi sai đề?
d.
\(3x-28=x+36\)
\(\Leftrightarrow2x=28+36\)
\(\Leftrightarrow2x=64\)
\(\Leftrightarrow x=32\)
e.
\(\left(-12\right)^2.x=56+10.13x\)
\(\Leftrightarrow144x=56+130x\)
\(\Leftrightarrow144x-130x=56\)
\(\Leftrightarrow14x=56\)
\(\Leftrightarrow x=4\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{7}{9}+\frac{5}{12}-\frac{3}{4}\)
\(=\frac{7x4}{36}+\frac{5x3}{36}-\frac{3x9}{36}\)
\(=\frac{28+15-27}{36}\)
\(=\frac{16}{36}=\frac{4}{9}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
A.35 x 34 + 35 x 38 + 65 x 75 + 65 x 45
Câu này không tính hợp lí được
B. 12x 53 + 53 x 172 - 53 x 84
= 53 x (12 + 172 - 84)
= 53 x 100
= 5300
C. 36 x 28 + 36 x 82 + 64 x 69 + 64 x 41
= 36 x (28+82) + 64 x (69+41)
= 36 x 110 + 64 x 110
= (36+64) x 110
= 100 x 110
= 11 000
D. A = 1+2+3+...+100
= (1+ 100) x 50
= 101 x 50
= 5050
E. B =17+19+...+101+103
= (103 +17) x [(103 - 17):2 + 1]
= 120 x 44
=5280
G. D= 3x (12+13+14+15) + 3x(8+7+6+5)
= 3 x (5+6+7+8+12+13+14+15)
= 3 x (20 x 4)
= 3 x 80
=240
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(58+7x=100\)
\(=>7x=100-58\)
\(=>7x=42\)
\(=>x=42:7\)
\(=>x=6\)
b) \(3x-7=28\)
\(=>3x=28+7\)
\(=>3x=35\)
\(=>x=35:3\)
\(=>x=\dfrac{35}{3}\)
c) \(x-56:4=16\)
\(=>x-14=16\)
\(=>x=16+14\)
\(=>x=30\)
d) \(101+\left(36-4x\right)=105\)
\(=>36-4x=105-101\)
\(=>36-4x=4\)
\(=>4x=36-4\)
\(=>4x=32\)
\(=>x=32:4\)
\(=>x=8\)
e) \(\left(x-12\right):12=12\)
\(=>x-12=12.12\)
\(=>x-12=144\)
\(=>x=144-12\)
\(=>x=132\)
f) \(\left(3x-2^4\right).7^3=2.7^4\)
\(=>3x-2^4=2.7^4:7^3\)
\(=>3x-16=2.7=14\)
\(=>3x=14+16\)
\(=>3x=30\)
\(=>x=30:3\)
\(=>x=10\)
i) \(\left(10+2x\right).4^{2011}=4^{2013}\)
\(=>10+2x=4^{2013}:4^{2011}\)
\(=>10+2x=4^2=16\)
\(=>2x=16-10\)
\(=>2x=6\)
\(=>x=6:2\)
\(=>x=3\)
\(#WendyDang\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(x-36:12=28\)
\(x-3=28\)
\(x=28+3\)
\(x=31\)
bài trên bị nhầm
![](https://rs.olm.vn/images/avt/0.png?1311)
a) Ta có:
\(x:10\) dư 7 \(\Rightarrow x+3⋮10\)
\(x:15\) dư 12 \(\Rightarrow x+3⋮15\)
\(x_{MIN};x+3⋮10;15\)
\(\Rightarrow x+3\in BCNN\left(10;15\right)\)
\(BCNN\left(10;15\right)=30\)
\(\Rightarrow x=27\)
b) \(36:x\) dư 6 \(\Rightarrow36-6⋮x\Rightarrow30⋮x\left(x>6\right)\)
\(46:x\) dư 1 \(\Rightarrow46-1⋮x\Rightarrow45⋮x\left(x>1\right)\)
\(\Rightarrow x\in UC\left(30;45\right)\)
\(UCLN\left(30;45\right)=15\)
c) \(x:15\)dư 8 \(\Rightarrow x+7⋮15\)
\(x:35\) dư 28 \(\Rightarrow x+7⋮35\)
\(\Rightarrow x+7\in BC\left(15;35\right)\)
\(BCNN\left(15;35\right)=105\)
\(B\left(105\right)=\left\{0;105;210;420;525;....\right\}\)
\(x< 500\)
(bài này thiếu dữ kiện đề nhé)
2) \(3x-5⋮x-1\)
\(3x-3-2⋮x-1\)
\(3\left(x-1\right)-2⋮x-1\)
\(3\left(x-1\right)⋮x-1\Rightarrow2⋮x-1\)
\(\Rightarrow x-1\inƯ\left(2\right)\)
\(Ư\left(2\right)=\left\{\pm1;\pm2\right\}\)
\(x\in\left\{2;0;-1;3\right\}\)
3x-28=x+36
=>3x-x=28+36
=>2x=64
=>\(x=\dfrac{64}{2}=32\)