`13 . (y + 3) - 9.( y+5) + (y+7) = 100`

`=> 13y + 39 - 9y - 45 + y+7 = 100`

`=> (13y - 9y  + y)+ 39 - 45+7 = 100`

`=> 5y + 1 = 100`

`=> 5y = 100 - 1`

`=> 5y = 99`

`=> y =` \(\dfrac{99}{5}\)

`A = 142 - [50-(2^3 - 10 - 2^3 . 5)]`

`A = 142 - [50-(8 - 10 - 8 . 5)]`

`A = 142 - [50-(-2 - 40)]`

`A = 142 - [50-(-42)]`

`A = 142 - (50+42)`

`A = 142 - 50-42`

`A = (142 - 42) - 50`

`A = 100 - 50`

`A = 50`

`(7 + 5y) : 2 + 13 = 19`

`=> (7 + 5y) : 2 = 19 - 13`

`=> (7 + 5y) : 2 = 6`

`=> 7 + 5y = 6 . 2`

`=> 7 + 5y = 12`

`=> 5y = 12 - 7`

`=> 5y = 5`

`=> y = 5 : 5`

`=> y = 1`

\(C=2+2^2+2^3+...+2^{100}\\ 2C=2^2+2^3+2^4+...+2^{101}\\ 2C-C=\left(2^2+2^3+2^4+...+2^{101}\right)-\left(2+2^2+2^3+...+2^{100}\right)\\ C=2^{101}-2\)

C = \(2+2^2+...+2^{100}\)

2C =\(2^2+2^3+...+2^{101}\)

2C - C = \(\left(2^2+2^3+...+2^{101}\right)-\left(2+2^2+...+2^{100}\right)\)

C = \(2^{101}-2\)

8 : 24 + 26 = \(\dfrac{1}{3}\) + 26 = \(\dfrac{1}{3}\) + \(\dfrac{78}{3}\) = \(\dfrac{79}{3}\)

4x+x-15=55

=>5x=55+15=70

=>\(x=\dfrac{70}{5}=14\)

= 4.x+x=55-15

=4.x+x=40

=x(4+1)=40

=x.5=40

=x=40:5

=x=8

Chúc bạn học tốt ^^

\(5n+12⋮n-5\)

=>\(5n-25+37⋮n-5\)

=>\(37⋮n-5\)

=>\(n-5\in\left\{1;-1;37;-37\right\}\)

=>\(n\in\left\{6;4;42;-32\right\}\)

mà n>=0

nên \(n\in\left\{6;4;42\right\}\)

`5n + 12 ⋮ n - 5`

`=> 5n - 25 + 37  ⋮ n - 5`

`=> 5(n - 5) + 37  ⋮ n - 5`

Do `n+5  ⋮ n - 5 `

`=> 5(n+5)  ⋮ n - 5`

`=> 37  ⋮ n - 5`

`=> n - 5` thuộc `Ư(37) =` {`-37;-1;1;37`}

`=> n` thuộc {`-32;4;6;42`}

Mà `n` thuộc `N`

`=> n` thuộc {`4;6;42`}

Vậy ...

\(\overline{abc0cd}\\ =a\cdot100000+b\cdot10000+c\cdot1000+0\cdot100+c\cdot10+d\\ =a\cdot10^5+b\cdot10^4+c\cdot10^3+0\cdot10^2+c\cdot10+d\)

\(\overline{abc0cd}=a\cdot10^5+b\cdot10^4+c\cdot10^3+0\cdot10^2+c\cdot10+d\)

\(=a\cdot10^5+b\cdot10^4+c\left(10^3+10\right)+d\)

a: \(11^2=11\cdot11=121;111^2=12321\)

b: Dự đoán: \(1111^2=1234321\)

Tính: \(1111^2=1111\cdot1111=1234321\)

trình bày và giải thích giups em đk ạ