`5^3-5^2(x-11)=10^2`

`=> 125-5^2(x-11)=100`

`=> 25(x-11)=125-100`

`=> 25(x-11)=25`

`=> x-11=1`

`=> x=12`

Vậy `x=12`

Đặt `A=(3n+10)/(n+2)`

`=> A= (3(n+2) + 4)/(n+2)`

`=> A = 3+ 4/(n+2)`

Để`3n+10 ⋮n+2`

`=> 4⋮n+2`

`=> n+2∈Ư(4)`

`=> n+2∈{-4;-2;-1;1;2;4}`

`=> n ∈{-6;-4;-3;-1;0;2}`

Vậy ....

`3^4 *(15+2x)=3^7`

`=> 15+2x=3^7:3^4=3^(7-4)`

`=> 15+2x=3^3`

`=> 15+2x=27`

`=> 2x=27-15`

`=> 2x=12`

`=> x=6`

Vậy `x=6`

`a)( -5/7)+7,45+12/7-2,45`

`=(-5/7 +12/7)+(7,45-2,45)`

`=1+5=6`

`b)7/12* (-2,34)- 7/12 * (-0,34)`

`=7/12 *[(-2,34)+0,34]`

`=7/12 *(-2)`

`=-7/6`

`c)0,75 *6/13+3/4 *7/13-2,75`

`=3/4*6/13+3/4 *7/13-2,75`

`=3/4*(6/13+7/13)-2,75`

`=3/4*1-11/4`

`=3/4-11/4`

`=(3-11)/4`

`=(-8)/4=-2`

chu vi đáy bể cá là

`(60+30)xx 2=180(cm)`

diện tích xung quanh bể cá là:

`180xx40=7200(cm^2)`

Đổi `20l=20dm^3=20000cm^3`

chiều cao phần nước trong bể là:

`20000:(60xx30)=100/9(cm)`

Đáp số:....

`(2x-123)xx3=23`

`=> 2x-123=23:3`

`=> 2x-123=23/3`

`=> 2x=23/3+123`

`=> 2x=23/3+369/3`

`=> 2x=392/3`

`=> x=392/3:2`

`=> x=196/3`

Vậy`x=196/3`

`(5x-1)(2x-1/3)=0`

`TH1:5x-1=0`

`=> 5x=1`

`=> x=1/5`

`TH2:2x-1/3=0`

`=> 2x=1/3`

`=> x=1/3 :2`

`=> x=1/3 xx 1/2=1/6`

Vậy ...

`2^(x-3) -3xx2^x=-92`

`=> 2^x *2^(-3) - 3xx2^x=-92`

`=>2^x*1/8 -3 xx 2^x=-92`

`=> 2^x xx(1/8-3)=-92`

`=> 2^x xx (-23/8) = -92`

`=> 2^x=(-92):(-23/8)`

`=> 2^x=32`

`=> 2^x=2^5`

`=> x=5`

Vậy `x=5`

`2^(x-3) -3xx2^x=-92`

`=> 2^x *2^(-3) - 3xx2^x=-92`

`=>2^x*1/8 -3 xx 2^x=-92`

`=> 2^x xx(1/8-3)=-92`

`=> 2^x xx (-23/8) = -92`

`=> 2^x=(-92):(-23/8)`

`=> 2^x=32`

`=> 2^x=2^5`

`=> x=5`

Vậy `x=5`

`37 xx 2 +2xx(x-1)=24`

`=> 74 +2xx(x-1)=24`

`=> 2xx(x-1)=24-74`

`=> 2xx(x-1)=-50`

`=> x-1=(-50):2`

`=> x-1=-25`

`=> x=(-25)+1=-24`

Vậy `x=-24`