`a)(x-2)(x^2+2x+4)-x(x-3)(x+3)=26`

`<=>x^3-2^3-x(x^2-9)=26`

`<=>x^3-8-x^3+9x=26`

`<=>9x-8=26`

`<=>9x=34`

`<=>x=34/9`

`b)(x-3)(x^2+3x+9)-x(x+4)(x-4)=21`

`<=>x^3-3^3-x(x^2-16)=21`

`<=>x^3-27-x^3+16x=21`

`<=>16x-27=21`

`<=>16x=48`

`<=>x=3`

\(a.\dfrac{1}{4}+\dfrac{3}{4}x=-0,3\)

\(\Leftrightarrow\dfrac{3}{4}x=-\dfrac{11}{20}\)

\(\Leftrightarrow x=-\dfrac{11}{15}\)

\(b.\dfrac{4}{7}x-\dfrac{7}{3}=\dfrac{1}{21}\)

\(\Leftrightarrow\dfrac{4}{7}x=\dfrac{50}{21}\)

\(\Leftrightarrow x=\dfrac{25}{6}\)

\(\Leftrightarrow\dfrac{6}{16}\cdot2< x< \dfrac{20}{21}\cdot\dfrac{21}{4}=5\)

=>3/4<x<5

hay \(x\in\left\{1;2;3;4\right\}\)

a  21-4x=13
  -4x=13-21
-4x=-8
x=-8/-4
x=2
 

b x=5

  chúc bạn học tốt

CÂU 1 TÍNH RA KHẮC BIẾT

CÂU 2 TA CÓ:    X/3 + X/4 = 21/ 12

                         X.(1/3 + 1/4) = 7/4

                         X. 7/12      = 7/4

                           X = 3

\(\dfrac{4}{x}=\dfrac{y}{21}=\dfrac{28}{49}=\dfrac{28:7}{49:7}=\dfrac{4}{9}\\ Vậy:x=\dfrac{4.9}{4}=9\\ y=\dfrac{4.21}{9}=\dfrac{28}{3}\)

\(\dfrac{x}{2}=\dfrac{3}{y}\\ \Leftrightarrow x.y=2.3=6\\ Vậy:\left[{}\begin{matrix}\left(x;y\right)=\left(1;6\right)=\left(6;1\right)\\\left(x;y\right)=\left(2;3\right)=\left(3;2\right)\end{matrix}\right.\)

\(3,\\ \dfrac{42}{54}=\dfrac{42:6}{54:6}=\dfrac{7}{9}\\ \dfrac{42}{54}=\dfrac{7}{x}=\dfrac{7}{9}\\ Vậy:x=\dfrac{7.9}{7}=9\)

a) x-15+124=200

x-15=200-124

x-15=76

x=76+15

x=91

Vậy x=91.

b) 3x-21=3⁶:3⁴

3x-21=3²

3x-21=9

3x=9+21

3x=30

x=30:3

x=10

Vậy x=10.

c) x-48:16=21

x-3=21

x=21+3

x=24

Vậy x=24.

a,(x-15)+124=200

   x - 15         = 200 - 124

  x - 15          = 76

  x                  = 76 + 15

  x                  = 91.

Vậy x = 91.

b,3x-21=3⁶:3⁴

   3x - 21 = 3²

    3x - 21 = 9

     3x       = 9 + 21

     3x       = 30

      x         = 30 : 3

      x         = 10.

Vậy x = 10.

c,x-48:16=21

    x - 3    = 21

     x         = 21 + 3

     x         = 24.

Vậy x = 24

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