Tìm x ∈ N

a) 2x chia hết cho 12 ⇒ 2x ∈ B(12) 

2x chia hết cho 30 ⇒ 2x ∈ B(30) 

Mà x có hai chữ số ⇒ 10 ≤ x ≤ 99 

\(\Rightarrow2x\in BC\left(12;30\right)\)

Mà: \(B\left(12\right)=\left\{0;12;24;36;48;60;72;84;96;108;...\right\}\)

\(B\left(30\right)=\left\{0;30;60;90;120;...\right\}\)

\(\Rightarrow BC\left(12;30\right)=\left\{0;60;...\right\}\)

\(\Rightarrow2x=60\)

\(\Rightarrow x=\dfrac{60}{2}\\ \Rightarrow x=30\)

b) \(9^{x+2}-9^{x+1}+9^x=657\)

\(\Rightarrow9^x\cdot\left(9^2-9+1\right)=957\)

\(\Rightarrow9^x\cdot\left(81-8\right)=657\)

\(\Rightarrow9^x\cdot73=657\)

\(\Rightarrow9^x=9\)

\(\Rightarrow9^x=9^1\)

\(\Rightarrow x=1\)

\(\frac{252}{y}=\frac{84}{5}\)ta có tử số : 252 : 84 = 3 | tức là Ps\(\frac{84}{5}=\frac{84\times3}{5\times3}=\frac{252}{15}\left(y=15\right)\)

\(y-\frac{2}{255}=\frac{38}{51}\)

\(y=\frac{38}{51}-\frac{2}{255}=\frac{188}{255}\)

              Bài làm

a) 252​​/y=84/5

Vì 252 : 3 = 84

=> y : 3 =5 

      y      = 5 x 3

      y      = 15

Vậy y = 15

b) y - 2/225  = 38/51

     y             = 38/51 + 2/225

     y             = 2884/3825

  Vậy y = 2884/3825

= 4/45

4/45 bạn nha

4/45 tk mk nhé cảm ơn bạn

a ) x/2=y/5 suy ra x/4=y/10

x/4=z/3 suy ra x/4=2z/3

suy ra x/4=y/10=2z/3=x+y-2z/4+10-6=8/8=1

x/4=1 suy ra x=1*4=4

y/10=1 suy ra y=10*1=10

z/3=1 suy ra z=3*1=3

\(y+\frac{23}{45}=\frac{51}{85}\Rightarrow y=\frac{51}{85}-\frac{23}{45}\Rightarrow y=\frac{4}{45}\)

51/85=y+23/45

      y =51/85-23/45

      y =2295/3825-1955/3825

      y =340/3825=4/45

=>x(0,2+0,5+0,25+1)=45

=>x*1,95=45

=>x=300/13

=4/45

ai k mk mk k lai cho

y=4/45 pạn ạ 

4/45 nha