1, x^2 . x^3 = 3^7 : 3^2

       x^5     = 3^5

=> x = 3

2, x - 18 : 3 = 12

    x - 6       = 12

    x            = 12 + 6

    x            = 18

3, (x - 18) : 2 = 12

     x - 18       = 12 . 2

     x - 18       = 24

     x             = 24 + 18

     x             = 42

4, x^2 = 16

    x^2 = 4^2

=> x = 4

x=4 nha bn

k k nha

mk k lại cho!

a, x+7=12

x=12-7

x=5

b, x-15=-21

x=-21+15

x=-6

c, 17-(x-9)=12

x-9=17-12

x-9=5

x=5+9

x=14

d, \(\left|x\right|+\left|-35\right|=41\)

\(\left|x\right|+35=41\)

\(\left|x\right|=41-35\)

\(\left|x\right|=6\)

\(\Rightarrow x=6\) hoặc \(x=-6\)

Vậy \(x\in\left\{6;-6\right\}\)

e, \(\left|x+3\right|=6\)

=> x+3=6 hoặc x+3=-6

+) x+3=6

x=6-3

x=3

+) x+3=-6

x=(-6)-3

x=-3

f, \(\left|-11\right|-\left|2-x\right|=9\)

\(11-\left|2-x\right|=9\)

\(\left|2-x\right|=11-9\)

\(\left|2-x\right|=2\)

\(\Rightarrow2-x=2\) hoặc \(2-x=-2\)

+) 2-x=2

x=2-2=0

+) 2-x=-2

x=2-(-2)=4

Thanks nhiều nha Nguyễn Quỳnh Chi

b, \(\dfrac{x-3}{4}=\dfrac{15}{20}\)

<=> \(\dfrac{x-3}{4}=\dfrac{3}{4}\)

=> x-3=3

<=> x=6

Vậy x=6

\(a,\dfrac{x}{15}=\dfrac{4}{y}=\dfrac{-2}{5}\)

* \(\dfrac{x}{15}=\dfrac{-2}{5}\)

\(\Rightarrow\dfrac{x}{15}=\dfrac{-6}{15}\)

\(\Rightarrow x=-6\)

*\(\dfrac{4}{y}=\dfrac{-2}{5}\)

\(\Rightarrow\dfrac{4}{y}=\dfrac{4}{-10}\)

\(\Rightarrow y=-10\)

Vậy x = - 6 ; y = - 10

\(b,\dfrac{x-3}{4}=\dfrac{15}{20}\)

=> ( x - 3 ) . 20 = 4. 15

=> 20x - 60 = 60

=> 20x = 60 + 60

=> 20x = 120

=> x = 120 : 20

=> x = 6

Vậy x = 6

\(c,\dfrac{-5}{9}+\dfrac{-8}{15}+\dfrac{22}{-9}+\dfrac{-7}{15}< x\le\dfrac{-1}{3}+\dfrac{-1}{4}+\dfrac{-5}{12}\)

\(\Rightarrow\dfrac{-5}{9}+\dfrac{-8}{15}+\dfrac{-22}{9}+\dfrac{-7}{15}< x\le\dfrac{-4}{12}+\dfrac{-3}{12}+\dfrac{-5}{12}\)

\(\Rightarrow\left(\dfrac{-5}{9}+\dfrac{-22}{9}\right)+\left(\dfrac{-8}{15}+\dfrac{-7}{15}\right)< x\le-1\)

\(\Rightarrow-3+\left(-1\right)< x\le-1\)

\(\Rightarrow-4< x\le-1\)

\(\Rightarrow x=-3;-2;-1\)

a, 14-3x = -x + 4

-3x + x = 4-14

-2x  = -12

 2x =12

x= 6

b, x-12  = -9--15

x-12 = 6

x=18

c, 16- I 5 - 2xI = 9

I 5 -2x I = 16-9

I 5-2x I = 7

\(\hept{\begin{cases}5x-2x=7\\5x-2x=-7\end{cases}}\hept{\begin{cases}2x=-2\\2x=12\end{cases}}\)

\(\hept{\begin{cases}x=-1\\x=6\end{cases}}\)

hok tốt

a: =>15-(x-2)=-13-27=-40

=>x-2=15+40=55

hay x=57

b: =>5-x=-114+12=-102

=>x=107

c: \(\Leftrightarrow\left|x\right|=-1-5=-6\)(vô lý)

d: \(\Leftrightarrow\left|x-3\right|=3\)

=>x-3=3 hoặc x-3=-3

=>x=6 hoặc x=0

a.Áp dụng t/c dãy tỉ số bằng nhau:

\(\dfrac{42+x}{30+x}=\dfrac{6}{7}\)

<=> 7(42+x) = 6(30+x)

<=> 294 + 7x = 180 + 6x

<=> x = -114

b.Áp dụng t/c dãy tỉ số bằng nhau:

\(\dfrac{x+15}{8}=\dfrac{x-12}{9}\)

<=> 9(x+15) = 8(x-12)

<=> 9x + 135 = 8x - 96

<=> x = -231

a)

2 - x = 17 - (-5)

2 - x = 22

x = 2 - 22

x = (-20)

b)

b)x-12=-9-15

x-12=-24

x=(-24)+12

x=-12

a. \(2-x=17-\left(-5\right)\)

\(\Leftrightarrow2-x=22\)

\(\Leftrightarrow x=2-22\)

\(\Leftrightarrow x=-20\)

b. \(x-12=\left(-9\right)-15\)

\(\Leftrightarrow x-12=-24\)

\(\Leftrightarrow x=-24+12\)

\(\Leftrightarrow x=-12\)

Biết rồi mà đi đố người khác . Chịu chị luôn em lạy 2 tay

tìm n   N để \(\frac{n}{n+1}\) + \(\frac{n}{n+2}\) là số tự nhiên

giúp mik với sắp thi r

\(\Leftrightarrow3\cdot\left(1+2+3+...+x\right)=3\times210.\)

\(\Leftrightarrow1+2+3+...+x=210\Leftrightarrow\frac{x\cdot\left(x+1\right)}{2}=210\)

\(\Leftrightarrow x\left(x+1\right)=420=20\times21\)

=> x = 20