125x[x+3]=9871

         x+3 =9871:125

         x+3=78,968

            x=78,968-3

            x=75,968

k mik nhe

125 x ( x + 3) = 9871

            x + 3  = 9871 : 125

            x + 3  = 78,968

                  x  = 78,968 - 3

                  x  = 75,968

125.(x+3)=9871

<=> x + 3 =78,968

<=> x = 75,968

=11111+1111111117

=222222222222227

 1239+9871+456789123+65432187

=(1239+9871)+(456789123+65432187)

=11110+522221310

=522232420

số 

to 

nắm

=>x:7/11=5/7

hay x=5/11

\(x:\dfrac{7}{11}=\dfrac{5}{7}\Leftrightarrow x=\dfrac{5}{7}.\dfrac{7}{11}=\dfrac{5}{11}\)

\(x:\dfrac{7}{11}=\dfrac{5}{7}\\ x=\dfrac{5}{7}\times\dfrac{7}{11}\\ x=\dfrac{35}{77}\)

nhân 7 vào F òi thu gọn

F=7 + 7² + 7³ + ... + 7¹⁰⁰

7F= 7² + 7³ + 7⁴ + ... + 7¹⁰¹

7F- F = (7² + 7³ + 7⁴ + ... + 7¹⁰¹)-(7 + 7² + 7³ + ... + 7¹⁰⁰)

6F=7¹⁰¹ - 7

thay vào biểu thức 6F + 7 = 7ⁿ ta được

(7¹⁰¹ - 7) + 7 =  7ⁿ 

 7¹⁰¹ - 7 + 7 = 7ⁿ

 7¹⁰¹ = 7ⁿ

^{=> n= 101}

https://hoc24.vn/cau-hoi/7-72-73-7100tim-so-tu-nhien-n-biet-6f-7-7n.6197530511708

`F = 7+7^2+....+7^{100}`

`=> 7F = 7^2 + 7^3+....+7^{101}`

`=> 6F = 7F - F = (  7^2 + 7^3+....+7^{101})-(7+7^2+....+7^{100})`

`=> 6F = 7^{101} - 7`

`=> 6F + 7 = 7^{101}-7+7=7^{101} = 7^n` nên `n = 101`

Vậy `n=101`

https://hoc24.vn/cau-hoi/7-72-73-7100tim-so-tu-nhien-n-biet-6f-7-7n.6197530511708

\(A=7.2+7.7+7.5-7.4\)

\(=14+49+35-28\)

\(=70\)

a=7(2+7+5-4)

a=7*10

a=10

a = 7 x 2 + 7 x 7 + 7 x 5 - 7 x 4

a = 7 x ( 2 + 7 + 5 - 4 )

a = 7 x 10

a = 70

~Học Tốt~

\(a=7\cdot2+7\cdot7+7\cdot5-7\cdot4\)

\(a=7\cdot\left(2+7+5-4\right)\)

\(a=7\cdot10\)

\(a=70\)

 a=7*2+7*7+7*5-7*4

a=14+49+35-28

a=98-28

a= 70

#Trl :

\(a=7\times2+7\times7+7\times5-7\times4\)

\(a=7\times\left(2+7+5-4\right)\)

\(a=7\times10\)

\(a=70\)