b) 4x – 10 = 15- x c) – 12 + x = 5x – 20 d) 7x – 4 = 20 + 3x e) 5x – 7 = -21 – 2x f) x + 15 = 7 – 6x g) 17 – x = 7-6x h) 3x + ( – 21) = 12 – 8x

0 bình luận về “b) 4x – 10 = 15- x c) – 12 + x = 5x – 20 d) 7x – 4 = 20 + 3x e) 5x – 7 = -21 – 2x f) x + 15 = 7 – 6x g) 17 – x = 7-6x h) 3x + ( – 21) = 12 – 8x”

1. b,

   $4x-10=15-x$

   $⇔4x+x=15+10$

   $⇔5x=25$

   $⇔x=5$

   Vậy $x=5$

   c,

   $-12+x=5x-20$

   $⇔5x-x=-12+20$

   $⇔4x=8$

   $⇔x=2$

   Vậy $x=2$

   d,

   $7x-4=20+3x$

   $⇔7x-3x=20+4$

   $⇔4x=24$

   $⇔x=6$

   Vậy $x=6$

   e,

   $5x-7=-21-2x$

   $⇔5x+2x=-21+7$

   $⇔7x=-14$

   $⇔x=-2$

   Vậy $x=-2$

   f,

   $x+15=7-6x$

   $⇔x+6x=7-15$

   $⇔7x=-8$

   $⇔x=-\dfrac{8}{7}$

   Vậy $x=-\dfrac{8}{7}$

   g,

   $17-x=7-6x$

   $⇔-x+6x=7-17$

   $⇔5x=-10$

   $⇔x=-2$
   Vậy $x=-2$

   h,

   $3x+(-21)=12-8x$

   $⇔3x+8x=12+21$

   $⇔11x=33$

   $⇔x=3$

   Vậy $x=3$

    

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2. b)

   4x-10=15-x

   4x+x=15+10

   5x=25

     x=5

   Vậy x=5

   c)

   -12+x=5x-20

   x -5x = -20 +12

   -4x = -8

       x = 2

   Vậy x = 2

   d)

   7x-4=20+3x

   7x -3x = 20 +4

   4x = 24

      x = 6

   Vậy x = 6

   e)

   5x-7=-21-2x

   5x +2x = -21 +7

   7x = -14

     x = -2

   Vậy x = -2

   f)

    x+15=7-6x

    x +6x = 7 -15

   7x = -8

      x = -$\frac{8}{7}$

   Vậy x = -$\frac{8}{7}$ ( nếu chưa học phân số thì x ∈ ∅ )

   g)

   17-x=7-6x

   x +6x = 7 -17

    7x = -10

   x =$\frac{10}{7}$

   Vậy x = -$\frac{10}{7}$ ( nếu chưa học phân số thì x ∈ ∅ )

   h)

   3x+(-21)=12-8x

    3x +8x = 12 +21

   11x = 33

    x = 3

     Vậy x = 3

    

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