Mình sửa lại, mình đọc nhầm đề bài:

\(\left(x-5\right)^{30}-\left(x-5\right)^{28}=0\)

\(\Rightarrow\left(x-5\right)^{28}\cdot\left[\left(x-5\right)^2-1\right]=0\)

\(\Rightarrow\left[{}\begin{matrix}\left(x-5\right)^{28}=0\\\left[\left(x-5\right)^2-1\right]=0\end{matrix}\right.\)

Xét \(\left(x-5\right)^{28}=0\Rightarrow x=5\)

Xét \(\left(x-5\right)^2-1=0\)

\(\Rightarrow\left[{}\begin{matrix}x-5=1\Rightarrow x=6\\x-5=-1\Rightarrow x=4\end{matrix}\right.\)

Vậy \(x\in\left\{4;5;6\right\}\)

\(\left(x-5\right)^{30}-\left(x-5\right)^{28}=0\)

\(\Rightarrow\left(x-5\right)^2=0\)

\(\Rightarrow x-5=0\)

\(\Rightarrow x=5\)

a ) x − 28   :   − 12   =   − 5 x − 28 =   − 5 .   − 12 x − 28     =  6 0   x   =  6 0   + 28 x   =  88

b ) x + 15   :   − 28   =  8 x + 15  = 8 . − 28 x + 15  = −  224   x   =   − 224  –  15 x   =   − 239

c ) x + 3 0   :   − 45   =   −  4 x + 3 0   =   − 4 .   − 45 x + 3 0   =  18 0 x   = 18 0   –  3 0 x   = 15 0

a) 2/5+9/5=11/5

b) 15/45+25/30=7/6

c) 28/32+45/72=3/2

d) 8/28+5/30=19/42

bài 2

a) x - 4/5 =4/5 + (3/7+3/5)

x-4/5=4/5+36/35

x-4/5=64/35

x=64/35+4/5

x=92/35

b) x-7/35=4/5

x=4/5+7/35

x=1

nhớ tk m nhé

a = 18/5

b = 3/9 + 5/6 = 6/18 + 25/18  = 31/18

c = 7/8 + 5/8 = 12/8

d = 4/14 + 1/6 = 14/42 + 7/42 = 21/42 -= 7/14

b2

x - 4/5 = 4.5 + ( 3/7 + 3/5 )

x - 4/5 = 49/35

           x = 49/35 + 4/5

              x = 77/35

x - 7/35 = 4/5

             x = 4/5 + 7/35

                 x = 1

mình ko chắc chắn đâu

mình nghĩ mình làm sai

xin lỗi làm nhầm

a: x:(-9)=-54

=>\(x=\left(-54\right)\cdot\left(-9\right)\)

=>\(x=54\cdot9=486\)

b: \(x:\left(-12\right)=18\)

=>\(x=18\cdot\left(-12\right)=-216\)

c: \(x:\left(-5\right)=-19\)

=>\(x:5=19\)

=>\(x=19\cdot5=95\)

d: \(\left(x-28\right):\left(-12\right)=-5\)

=>\(x-28=\left(-12\right)\cdot\left(-5\right)=60\)

=>x=60+28=88

e: \(\left(x+15\right):\left(-28\right)=8\)

=>x+15=-28*8=-224

=>x=-224-15=-239

f: (x+30):(-45)=-4

=>\(x+30=\left(-45\right)\cdot\left(-4\right)=180\)

=>x=180-30

=>x=150

a) x : (-9) = -54

x= -54 . (-9)= 486

________

b) x : (-12) = 18

x= 18. (-12)= -216

_________

c) x : (-5) = -19

x= (-19). (-5)= 95

__________

d) (x - 28) : (-12) = -5

(x-28)= (-5). (-12)= 60

x= 60+28= 88

_______

e) (x + 15) : (-28) = 8

(x+15)= 8. (-28)= -224

x= -224 - 15 = - 239

__________

f) (x + 30) : (-45) = -4

(x+30)= -4. (-45)= 180

x= 180 - 30=150

A = 29 x 5 x 30

B = 29 x 5 x 29

Vì 5 = 5 => Ta so sánh 29 x 29 và 28 x 30

28 x 30 = 30 x (29 - 1) = 30 x 29 -  30

29 x 29 = 29 x (30 - 1) = 29 x 30 - 29

Thấy: 30 x 29 - 30 < 30 x 29 - 29

Vậy 29 x 29 > 28 x 30 nên A < B     

Lời giải:

$7^{5x}:49=7^{28}$

$7^{5x}:7^2=7^{28}$

$7^{5x-2}=7^{28}$

$\Rightarrow 5x-2=28$

$\Rightarrow 5x=30$
$\Rightarrow x=6$

b.
$5^{2x}.5^{14}=5^{30}$

$5^{2x+14}=5^{30}$

$\Rightarrow 2x+14=30$

$\Rightarrow 2x=16$

$\Rightarrow x=8$

a) 7^5x:49=7^28

    7^5x:7^2=7^28

     7^5x=7^28.7^2

      7^5x=7^30

suy ra 5x=30

             x= 6

b) 5 mũ 2x. 5 mũ 14 =5 mũ 30

5^2x=5^16

suy ra 2x=16

x =16/2

x=8

A=(28x5)x30

A=140x(29+1)

A=140+140x29

B=(29x5)x29

B=145x29

B=(140+5)x29

B=140x29+5x29

B=140x29+145

=> A<B

A<B

k mình nha

câu trả lời là 

  a<b

   đs...

30+29+28+.......+2+1=(1+2+3+4+5).x

(30+1)x30:2=15.x

465=15.x

x=465:15

x=31

~shizadon~

Theo bài ra ta có: 
30 + 29 + 28 + ... + 2 + 1 = (1 + 2 + 3 + 4 + 5) . x
(30 + 1) x 30 : 2 = 15 . x
x = 465 : 15
x = 31

Theo bài ra ta có: 
30 + 29 + 28 + ... + 2 + 1 = (1 + 2 + 3 + 4 + 5) . x
(30 + 1) x 30 : 2 = 15 . x
x = 465 : 15
x = 31

=60X47+60X25+60X28

=60X(47+25+28)

=60X100=6000

=60* (47+25+28)

=60 nhân 100

=6000

5 X 47 X 12 + 4 X 15 X 25 + 2 X 28 X 30

=2820+1500+1680

=4320+1680

=6000

MIK LÀM RỒI,ĐÚNG 100%