\(a)x=\dfrac{1}{4}+\dfrac{5}{13}=\dfrac{33}{52}.\\ b)\dfrac{x}{3}=\dfrac{2}{3}+\dfrac{-1}{7}.\\ \Leftrightarrow\dfrac{x}{3}=\dfrac{11}{21}.\\ \Leftrightarrow\dfrac{7x}{21}=\dfrac{11}{21}.\\ \Rightarrow7x=11.\\ \Leftrightarrow x=\dfrac{11}{7}.\\ c)\dfrac{x}{3}=\dfrac{16}{24}+\dfrac{24}{36}=\dfrac{2}{3}+\dfrac{2}{3}=\dfrac{4}{3}.\\ \Rightarrow x=4.\\ d)\dfrac{x}{15}=\dfrac{1}{5}+\dfrac{2}{3}=\dfrac{13}{15}.\\ \Rightarrow x=13.\)

a) ( x - 266 ): 5 = 7 

    ( x - 266 )     = 7 x 5

    ( x - 266 )     =  35     

      x                 = 35 + 266

      x                 = 301

b) ( x - 129 ) x 4 = 36

    ( x - 129 )       = 36 : 4

    ( x - 129 )       = 9

      x                   = 9 + 129

      x                   = 138

c) 786 - x = 5 x 4 : 2

    786 - x = 20 : 2

    786 - x = 10

             x = 786 - 10

             x = 776

d) x + 24 : 4 x 3 = 285

    x + 6 x 3        = 285

    x + 18            = 285

    x                    = 285 - 18 

    x                    = 267

x^2 = 5/7 *x 

x*x = 5/7 *x 

x* x :x = 5/7

x= 5/7

\(x^2=\frac{5}{7}x\)

\(=>x=\frac{5}{7}\)

Vậy pt trên có nghiệm là \(\frac{5}{7}\)

a) {-2).x = -10 => x = (-10): (- 2) => x = 5.

b)  (-18). x = -36 => x = (-36): (-18) => x = 2.

c) 2.x + 1 = 3=>2x = 2 => x = l.

d) (-4).x + 5 = -15 => (-4)x = (-15) -5 => (-4) x = -20 => x = 5.

a) {-2).x = -10 => x = (-10): (- 2) => x = 5.

b)  (-18). x = -36 => x = (-36): (-18) => x = 2.

c) 2.x + 1 = 3=>2x = 2 => x = l.

d) (-4).x + 5 = -15 => (-4)x = (-15) -5 => (-4) x = -20 => x = 5.

a, 1 + 2 + ... + x = 45

=> x ( x + 1) / 2 = 45

=> x ( x + 1) = 90

=> x ( x + 1) = 9 .10

=> x = 9

b, tương tự

a. x=9

b. x=8

Ta có : 1 + 2 + 3 + ...... + x = 45

=> x(x + 1) : 2 = 45

=> x(x + 1) = 90

=> x(x + 1) = 9.10

=> x = 9 

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

\(a,-45:5\cdot\left(-3-2x\right)=3\\ \Leftrightarrow-9\cdot\left(-3-2x\right)=3\\ \Leftrightarrow-2x-3=-\dfrac{1}{3}\\ \Leftrightarrow2x+3=\dfrac{1}{3}\\ \Leftrightarrow2x=-\dfrac{8}{3}\\ \Leftrightarrow x=-\dfrac{4}{3}\\ b,3x-28=x+36\\ \Leftrightarrow2x=64\\ \Leftrightarrow x=32\\ c,\left(-12\right)^2x=56+10\cdot13x\\ \Leftrightarrow144x=56+130x\\ \Leftrightarrow14x=56\\ \Leftrightarrow x=4\)

a) \(1+2+...+x=45\)

\(\Rightarrow\frac{x\left(x+1\right)}{2}=45\)

\(\Rightarrow x\left(x+1\right)=90\)

\(\Rightarrow x\left(x+1\right)=9\cdot10\)

VẬy x = 9

a,x=9                                                   b,x=11nha bạn

a)36 chia -3 =x

b)(-100):x=-5+-5

(-100):x=-10

(-100):10=x

(-100): -10 =x nha anh ấn nhầm

a: \(\Leftrightarrow3x+9=-2x+6\)

=>5x=-3

hay x=-3/5

b: =>3/x=y/35=3/7

=>x=7; y=15

c: =>9x/5=-3/5

=>9x=-3

hay x=-1/3

d: =>x+2/26=-1/4

=>x+2=-13/2

hay x=-17/2