a: \(2x+3x=5^7:5\)

=>\(5x=5^7:5=5^6\)

=>\(x=5^6:5=5^5\)

b: \(7\left(42-x\right)=5^3+134\)

=>7(42-x)=125+134=259

=>42-x=37

=>x=42-37=5

c: \(x+18:3^2=5\cdot4^2\)

=>\(x+\frac{18}{9}=5\cdot16\)

=>x+2=80

=>x=80-2

=>x=78

42 - ( 2x +32) + 18/3 =0 <=> 42 - 2x -32 +18/3 =0 <=> -2x +10 +18/3 =0 <=> 2x = 16 <=> x=8

\(A=a+\left(42-70+18\right)-\left(42+18-a\right)\)

\(A=a+42-70+18-42-18-a\)

\(A=\left(a-a\right)+\left(42-42\right)+\left(18-18\right)-70\)

\(A=0+0+0-70=-70\)

mk cần câu c bạn nhé

ai trả lời mk cho k nhé

a) A = a + (42-70+18) - (42+18+a)

        = a + 42 - 70 + 18 - 42 - 18 - a

        = (a-a) + (42-42) + (18-18) - 70

        = 0 + 0 + 0 - 70 = -70.

Vậy A = -70.

b) B = a + 30 + 12 - (-20) + (-12) - (2+a)

        = a + 30 + 12 + 20 - 12 - 2 - a

        = (a-a) + (12-12) + (30+20-2)

        = 0 + 0 + (50-2)

        = 50 - 2 = 48.

Vậy B = 48.

c) C = (x-y+z) - (x-y-z) - (2x+y)

        = x - y + z - x + y + z - 2x - y

        = (x-x-2x) + (-y+y-y) + (z+z)

        = -2x + (-y) + 2z

        = -2x - y + 2z.

Vậy C = -2x - y + 2z.

\(-\dfrac{18}{42}\cdot\dfrac{35}{42}:\dfrac{-98}{42}\)

\(=-\dfrac{18}{42}\cdot\dfrac{35}{42}\cdot\dfrac{42}{-98}\)

\(=\dfrac{-18}{42}\cdot\dfrac{-5}{14}\\ =\dfrac{15}{98}\)

\(\dfrac{-18}{42}.\dfrac{3\text{5}}{42}:\dfrac{-98}{42}\)

\(=\dfrac{-18}{42}.\dfrac{3\text{5}}{42}.\dfrac{-42}{98}\)

\(=\dfrac{1\text{5}}{98}\)

Bài 2 Tìm x: a)   27-(27-x)=45 ,

27+x-27=45

x=45

b) -18+42=42-2x

24=42-2x

2x=42-14

2x=28

x=14

1)

a) (-38).47+147.38 

= 38.(147 - 47) 

= 38 . 100 = 3800

b) 37.42-142.37+15 

= 37.(42 - 142) + 15

= 37. (-100) + 15

= -3700 + 15 = -3685

c) 46.115-14.46+(-46) 

= 46.(115 - 14 - 1)

= 46 . 100 = 4600

2)

a) 27-(27-x) = 45

           27-x = 27 - 45

          27-x = -18

               x = 27 + 18

          => x = 45

Vậy x = 45

 b) -18+42=42-2x

             2x = 42 + 18 - 42

             2x = 18

          => x = 9

Vậy x = 9 

Chúc em học tốt!!!

Sai

=a+(-28+18)-(42+18+a)

=a+(-10)-(60+a)

=a+(-10)-60-a

=(-10)-60

=(-70)