a) 2 * x - 138 = 8 * 9

2 * x - 138 = 72

2 * x = 210

x = 105

b) 231 - ( x - 6 ) = 1339 : 13

231 - x + 6 = 103

237 - x = 103

x = 134

c) 70 - 5 * ( x-3) = 45

5 * (x-3) = 25

x - 3 = 5

x = 8

cac phan con lai bn lm tuong tu nha

* 2*X-138=8*9

   <=> 2*X-138=72

   <=> 2*X=72+138

   <=> 2*X=210

   <=> X=210/2=105

*231-(X-6)=1339:13

 <=> 231-(X-6)=103

<=> X-6=231-103

<=>X-6=128

<=>X=128+6=134

*70-5*(X-3)=45

<=>5*(X-3)=70-45

<=>5*(X-3)=25  

<=>X-3=25/5

<=>X-3=5

<=>X=8

*10+2*X=16

<=>2*X=16-10

<=>2*X=6

<=>X=6/2=3

\(2x-138=72\)

\(2x=72+138\)

\(2x=210\)

\(x=105\)

\(231-\left(x-6\right)=103\)

\(x-6=231-103\)

\(x-6=128\)

\(x=134\)

\(5\left(x-3\right)=70-45\)

\(5\left(x-3\right)=25\)

\(x-3=5\)

\(x=5+3\)

\(x=8\)

\(2x=16-10\)

\(2x=6\)

\(x=3\)

\(5\times4\times2\times25\)

\(=\left(5\times2\right)\times\left(4\times25\right)\)

\(=10\times100=1000\)

________

\(138\times8+2\times138\)

\(=138\times\left(8+2\right)\)

\(=138\times10=1380\)

Bài3: Tính bằng cách thuận tiện nhất: 72,34×6,75+27,66×6,75=?

>_<

a)\(2.x-138=8.9\)

\(2.x-138=72\)

\(2.x=72+138\)

\(2.x=210\)

\(x=210\div2\)

\(x=105\)

b)\(\left\{\left(6x-72\right)\div2-84\right\}.28=5628\)

\(\left(6x-72\right)\div2-84=201\)

\(\left(6x-72\right)\div2=285\)

\(6x-72=570\)

\(6x=642\)

\(x=107\)

c)\(420+65.4=\left(x+175\right)\div5+30\)

\(420+260=\left(x+175\right)\div5+30\)

\(680=\left(x+175\right)\div5+30\)

\(650=\left(x+175\right)\div5\)

\(3250=x+175\)

\(3075=x\)

a) 2 * x - 138 = 72

    2 * x          = 72 + 138

    x                = 210 \ 2

    x                = 105

Mk thay x=y nha!!!

a)2xy-138=8x9

2xy-138=72

2xy=72+138

2xy=210

y=210:2

y=105

b){(6xy-72):2-84)}x28=5628

{(6xy-72):2-84)}x28=5628

{(6xy-72):2-84=201

{(6xy-72):2=285

(6xy-72)=570

6y=570+72

6y=642

=>y=107

c)420+65x4=(y+175):5+30

680=(y+175):5+30

650=(y+175):5

3250=y+175

y=3250-175

y=3075

`2 xx y - 138 = 2560`

`2 xx y = 2560 + 138`

`2 xx y = 2698`

`y = 1349`

Vậy `y = 1349`

2 x y - 138 = 80 + 8 x 4

      y = 2698 : 2

      y = 1349

\(2x-138-8\times3=2x-138-24=2x-162\)

๖ACE✪MVP༻꧂.thấy tên đẹp thi cho mình 1 tích

༺Ɗเευ༒Ƭɦυyεɳ༻

2 * (x + 7) - 16 = 18

2 * (x +7) = 18 + 16 = 34

x + 7 = 34 : 2 = 17

x = 17 - 7 = 10

(x - 8:2) = 165 - 75

x- 4 = 90

x = 90 + 4 = 94

4 * x + 2 * x = 138

x * (4 + 2) = 138

x * 6 = 138

x = 138 : 6 = 23

 (2 giờ 18 phút x 9+2,3 giờ x 6+138 phút x 5) : 10

= (     2,3 giờ    x 9 + 2,3 giờ x 6 +  2,3 giờ     ) : 10

= 2,3 giờ x (   9 + 6    )  : 10

= 2,3 giờ x       15          : 10

=            34,5  giờ          :  10

=        3,45 giờ

đang voi nen khong rai ra duoc . **** cho minh nhe