a.\(3+x=-8\)
\(x=-8-3\)
\(x=-11\)
b.\(\left(35+x\right)-12=27\)
\(35+x=27+12\)
\(35+x=39\)
\(x=39-35\)
\(x=4\)
c.\(2^x+15=31\)
\(2^x=31-15\)
\(2^x=16\)
\(2^x=2^4\)
\(x=4\)

câu a : 

3 + x = -8

x = -8 - 3

x = -11

câu b : 

(35 + x) - 12 = 27

35 + x = 39

x = 39 - 35

x = 4

câu c : 

2^x + 15 = 31

2^x = 31 - 15

2^x = 16

x = \(\sqrt{16}\) = 4

\(\frac{x}{4}=\frac{y}{3}\)

\(\Rightarrow\frac{x+y}{4+3}=\frac{x}{4}=\frac{y}{3}\) mà x + y = 14

\(\Rightarrow\frac{14}{7}=\frac{x}{4}=\frac{y}{3}\)

\(\Rightarrow2=\frac{x}{4}=\frac{y}{3}\)

\(\Rightarrow\hept{\begin{cases}x=2\cdot4=8\\y=2\cdot3=6\end{cases}}\)

a .   x   -   3 4   =   3 5 x   =   3 5   +   3 4 x = 27 20

b .   x   :   1 4 = 16 x = 16 x 1 4 x   =   4

Đáp án cần chọn là: D

−x–14+35=−26−(−11)

−x+21=−26+11

21–x=−15

x =21+15

x=36

\(35-\left|2x-1\right|=14\)

\(\Leftrightarrow\left|2x-1\right|=21\)

\(\Leftrightarrow\orbr{\begin{cases}2x-1=21\left(x\ge\frac{1}{2}\right)\\2x-1=-21\left(x< \frac{1}{2}\right)\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}2x=22\\2x=-20\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}x=11\left(TM\right)\\x=-10\left(TM\right)\end{cases}}\)

\(35-|2x-1|=14\)

\(|2x-1|=21\)

\(\Rightarrow\orbr{\begin{cases}2x-1=21\\2x-1=-21\end{cases}\Rightarrow\orbr{\begin{cases}2x=22\\2x=-20\end{cases}\Rightarrow}\orbr{\begin{cases}x=11\\x=-10\end{cases}}}\)

Ta có:[2x-1]=35-14

=>[2x-1]=21

=>2x=21+1

=>2x=22

=>x=22/2

=>x=11