Bài 2 :

a,  \(2^x+2^{x+4}=272\)   

    \(2^x+2^x.2^4=272\)

\(2^x.\left(1+2^4\right)=272\)

\(2^x.17=272\)

\(2^x=272:17\)

\(2^x=16=2^4\)

\(\Rightarrow x=4\)

1: Bài này hơi khó đó

\(\frac{1}{21}+\frac{1}{28}+\frac{1}{36}+...+\frac{1}{x\times\left(x+1\right)\div2}=\frac{2}{9}\)

\(\Rightarrow\frac{1}{6\times\left(6+1\right)\div2}+\frac{1}{7\times\left(7+1\right)\div2}+...+\frac{1}{x\times\left(x+1\right)\div2}=\frac{2}{9}\)

\(\Rightarrow\frac{1}{6\times7\div2}+\frac{1}{7\times8\div2}+...+\frac{1}{x\times\left(x+1\right)\div2}\)

\(\Rightarrow\frac{2}{6\times7}+\frac{2}{7\times8}+...+\frac{2}{x\times\left(x+1\right)}=\frac{2}{9}\)

\(\Rightarrow2\times\left(\frac{1}{6}+\frac{1}{7}-\frac{1}{7}+\frac{1}{8}-\frac{1}{8}+...+\frac{1}{x}-\frac{1}{x+1}\right)=\frac{2}{9}\)

\(\Rightarrow2\times\left(\frac{1}{6}-\frac{1}{x+1}\right)=\frac{2}{9}\)

\(\Rightarrow\left(\frac{1}{6}-\frac{1}{x+1}\right)=\frac{2}{9}\div2\)

\(\Rightarrow\frac{1}{6}-\frac{1}{x+1}=\frac{1}{9}\)

\(\Rightarrow\frac{1}{x+1}=\frac{1}{18}\)

=> x = 18 - 1

=> x = 17

Để có giá trị số nguyên => n + 1 chia hết cho n - 2

-> n + 1 - ( n - 2 ) chia hết cho n - 2

-> n + 1 - n + 2 chia hết cho n - 2 

-> n - 2 thuộc U ( 3 ) = ( - 1 ; 1 ; 3 ; - 3 )

em 12 tuoi

anh 36 tuổi

Giúp MK với bạn hùng sai rồi

chac co

\(y+\frac{1}{2}\cdot\frac{1}{3}=\frac{3}{4}\)

\(y+\frac{1}{6}=\frac{3}{4}\)

\(y=\frac{3}{4}-\frac{1}{6}\)

\(y=\frac{7}{12}\)

\(y\)\(+\)\(\frac{1}{2}\)X   \(\frac{1}{3}\)\(=\)\(\frac{3}{4}\)

\(y\)\(+\)\(\frac{1}{6}\)               \(=\)\(\frac{3}{4}\)

\(y\)                               \(=\)\(\frac{7}{12}\)

dấu nhân là dấu chấm nhé mọi người

Đề sai, phải như sau:

\(A=\frac{34,4\cdot6,34+3,66\cdot34,4}{17,2\cdot9,55+12,45\cdot17,2-17,2}\)

\(=\frac{34,4\left(6,34+3,66\right)}{17,2\left(9,55+12,45-1\right)}\)

\(=\frac{17,2\cdot2\cdot10}{17,2\cdot20}\)

\(=1\)