( 3x - 6 ) . 3 = 18

3x - 6 = 18 : 3 = 6

3x = 6 + 6 = 12

x= 4

6x - 5 = 613

6x = 613 + 5 =618

x=103

x-36:18=12

x - 2 = 12

x= 12 + 2

x= 14

\(\left(3x-6\right).3=18\)

\(\Rightarrow3x-6=19:3=6\)

\(\Rightarrow3x=6+6=12\)

\(\Rightarrow x=12:3=4\)

\(6.x-5=613\)

\(\Rightarrow6x=613+ 5=618\)

\(\Rightarrow x=618:6=103\)

\(x-36:18=12\)

\(\Rightarrow x-2=12\)

\(\Rightarrow x=12+2=14\)

Ủng hộ nha m.n ^_^

\(\Leftrightarrow3^{x-1}\left(1+3+3^2\right)=39\\ \Leftrightarrow3^{x-1}\cdot13=39\\ \Leftrightarrow3^{x-1}=3=3^1\\ \Leftrightarrow x-1=1\Leftrightarrow x=2\)

\(\Leftrightarrow3^x\cdot\dfrac{13}{3}=39\)

\(\Leftrightarrow x=2\)

\(\left(x-36\right):18=12\)

\(x-36=12x18\)

\(x-36=216\)

           \(x=216+36\)

           \(x=252\)

\(K\)\(nha!!!\)

x-36:18=12

=>x-2=12

=>x=12+2

=>x=14

Vậy x=14

\(\frac{36}{1\cdot3\cdot5}+\frac{36}{3\cdot5\cdot7}+\frac{36}{5\cdot7\cdot9}+...+\frac{36}{25\cdot27\cdot29}\)

\(=9\left[\frac{4}{1\cdot3\cdot5}+\frac{4}{3\cdot5\cdot7}+\frac{4}{5\cdot7\cdot9}+...+\frac{4}{25\cdot27\cdot29}\right]\)

\(=9\left[\frac{1}{1\cdot3}-\frac{1}{3\cdot5}+\frac{1}{3\cdot5}-\frac{1}{5\cdot7}+...+\frac{1}{25\cdot27}-\frac{1}{27\cdot29}\right]\)

\(=9\left[\frac{1}{3}-\frac{1}{783}\right]=9\cdot\frac{260}{783}=\frac{260}{87}\)

Đặt \(A=\frac{36}{1.3.5}+\frac{36}{3.5.7}+\frac{36}{5.7.9}+...+\frac{36}{25.27.29}\)

\(\Rightarrow\frac{1}{9}A=\frac{4}{1.3.5}+\frac{4}{3.5.7}+\frac{4}{5.7.9}+...+\frac{4}{25.27.29}\)

\(\Rightarrow\frac{1}{9}A=\frac{1}{1.3}-\frac{1}{3.5}+\frac{1}{3.5}-\frac{1}{5.7}+...+\frac{1}{25.27}-\frac{1}{27.29}\)

\(\Rightarrow\frac{1}{9}A=\frac{1}{1.3}-\frac{1}{27.29}\)

\(\Rightarrow\frac{1}{9}A=\frac{261}{783}-\frac{1}{783}\)

\(\Rightarrow\frac{1}{9}A=\frac{260}{783}\)

\(\Rightarrow A=\frac{260}{783}\div\frac{1}{9}\)

\(\Rightarrow A=\frac{2340}{783}=\frac{260}{87}\)

** Cần bổ sung thêm điều kiện $x,y$ là số nguyên.

Lời giải:

$xy-3x+y-3=5$

$(xy-3x)+(y-3)=5$

$x(y-3)+(y-3)=5$

$(x+1)(y-3)=5$

Do $x,y$ là các số nguyên nên $x+1, y-3$ cũng là số nguyên.

Khi đó ta có các TH sau:
TH1: $x+1=1, y-3=5\Rightarrow x=0; y=8$

TH2: $x+1=-1, y-3=-5\Rightarrow x=-2; y=-2$

TH3: $x+1=5, y-3=1\Rightarrow x=4; y=4$

TH4: $x+1=-5, y-3=-1\Rightarrow x=-6; y=2$

3x + 8 = 35

3x       =35 - 8

3x        =27

   x       = 27 : 3

   x        = 9.

Vậy x = 9.

3x + 8 = 35

3x       = 35 - 8

3x        = 27

  x        = 27 : 3

  x         = 9

Vậy x = 9

120 - 3x = - 40

3x = 120 - ( -40)

3x = 160

x = 160 : 3

x = 53,(3)

120-3x=-40

3x=120-(-40)

3x=120+40

3x=160

x=160:3

x=53,(3)