2:

a: x+201=351

=>x=351-201

=>x=150

b: \(8\cdot5^2-27:25\)

\(=8\cdot25-\dfrac{27}{25}\)

\(=200-1,08=198,92\)

d: \(2023-23:\left[9+2\left(2^3-0,21\right)\right]\)

\(=2023-23:\left[9+16-0,42\right]\)
\(=2023-\dfrac{23}{25-0,42}\)

\(=2023-\dfrac{1150}{1229}=\dfrac{2485117}{1229}\)

b: 2(x-21)=84

=>x-21=84/2=42

=>x=42+21=63

c: 135-4(81-x)=55

=>4(81-x)=135-55=80

=>81-x=20

=>x=61

\(a,-\dfrac{13}{20}+x=\dfrac{-11}{15}\\ \Rightarrow x=\dfrac{-11}{15}+\dfrac{13}{20}\\ \Rightarrow x=-\dfrac{1}{12}\\ b,\left(x-3,5\right):3\dfrac{1}{2}-2,5=-1\dfrac{3}{4}\\ \Rightarrow\left(x-\dfrac{7}{2}\right):\dfrac{7}{2}-\dfrac{5}{2}=\dfrac{-7}{4}\\ \Rightarrow\left(x-\dfrac{7}{2}\right):\dfrac{7}{2}=\dfrac{3}{4}\\ \Rightarrow x-\dfrac{7}{2}=\dfrac{21}{8}\\ \Rightarrow x=\dfrac{49}{8}\)

\(\left[{}\begin{matrix}x-1,5=0\\2,5-x=0\end{matrix}\right.\left[{}\begin{matrix}x=1,5\\x=2,5\end{matrix}\right.\)

\(\left[{}\begin{matrix}x-\dfrac{4}{5}=\dfrac{3}{4}\\x-\dfrac{4}{5}=\dfrac{-3}{4}\end{matrix}\right.\left[{}\begin{matrix}x=\dfrac{31}{20}\\x=\dfrac{1}{20}\end{matrix}\right.\)

c.x thuộc tập hợp rỗng

d. cậu chia ra thành 2 trường hợp nhé

Th1
x-1,5+2,5-x=0
<=>0x=-1
=> vô lí
Th2
-x+1,5-2,5+x=0
<=>0x=1
=>vô lí

vậy không có x thỏa mãn

Bài 1: 

a) Ta có: \(\dfrac{17}{6}-x\left(x-\dfrac{7}{6}\right)=\dfrac{7}{4}\)

\(\Leftrightarrow\dfrac{17}{6}-x^2+\dfrac{7}{6}x-\dfrac{7}{4}=0\)

\(\Leftrightarrow-x^2+\dfrac{7}{6}x+\dfrac{13}{12}=0\)

\(\Leftrightarrow-12x^2+14x+13=0\)

\(\Delta=14^2-4\cdot\left(-12\right)\cdot13=196+624=820\)

Vì Δ>0 nên phương trình có hai nghiệm phân biệt là:

\(\left\{{}\begin{matrix}x_1=\dfrac{14-2\sqrt{205}}{-24}=\dfrac{-7+\sqrt{205}}{12}\\x_2=\dfrac{14+2\sqrt{2015}}{-24}=\dfrac{-7-\sqrt{205}}{12}\end{matrix}\right.\)

b) Ta có: \(\dfrac{3}{35}-\left(\dfrac{3}{5}-x\right)=\dfrac{2}{7}\)

\(\Leftrightarrow\dfrac{3}{5}-x=\dfrac{3}{35}-\dfrac{10}{35}=\dfrac{-7}{35}=\dfrac{-1}{5}\)

hay \(x=\dfrac{3}{5}-\dfrac{-1}{5}=\dfrac{3}{5}+\dfrac{1}{5}=\dfrac{4}{5}\)

ai giúp mik vs

Bài 3: 

a) Ta có: \(2x-3=x+\dfrac{1}{2}\)

\(\Leftrightarrow2x-x=\dfrac{1}{2}+3\)

\(\Leftrightarrow x=\dfrac{7}{2}\)

b) Ta có: \(4x-\left(x+\dfrac{1}{2}\right)=2x-\left(\dfrac{1}{2}-5\right)\)

\(\Leftrightarrow3x-\dfrac{1}{2}-2x+\dfrac{1}{2}-5=0\)

\(\Leftrightarrow x=5\)

16: Chu vi hình bình hành là (6+8)*2=28(cm)

Diện tích hình bình hành là:

\(5\cdot6=30\left(cm^2\right)\)

14:

a: \(25+7\left(x-5\right)=123\)

=>\(7\left(x-5\right)=123-25=98\)

=>x-5=14

=>x=19

b: \(8^{3x-1}:8^x=512\)

=>\(8^{3x-2}=8^3\)

=>3x-2=3

=>3x=5

=>x=5/3(loại)

\(a,2x+34=56\\ \Rightarrow2x=56-34\\ \Rightarrow x=22:2\\ \Rightarrow x=11\\ b,87-\left(x-654\right):3=21\\ \Rightarrow\left(x-654\right):3=87-21\\ \Rightarrow x-654=66:3\\ \Rightarrow x=22+654\\ \Rightarrow x=676\\ c,7^{65}:7^x=7^{43}.7^{21}\\ \Rightarrow7^{65-x}=7^{43+21}\\ \Rightarrow65-x=64\\ \Rightarrow x=65-64\\ \Rightarrow x=1\)

\(a,\frac{3}{4}+\frac{1}{4}:x=\frac{2}{5}\)

\(\Leftrightarrow\frac{1}{4}:x=\frac{2}{5}-\frac{3}{4}\)

\(\Leftrightarrow\frac{1}{4}:x=\frac{8}{20}-\frac{15}{20}\)

\(\Leftrightarrow\frac{1}{4}:x=\frac{-7}{20}\)

\(\Leftrightarrow x=\frac{1}{4}.\frac{20}{-7}\)

\(\Leftrightarrow x=\frac{20}{-28}\)

\(b,|x-2,5|=1,5\)

\(\Leftrightarrow\orbr{\begin{cases}x-2,5=1,5\\x-2,5=-1,5\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}x=1,5+2,5\\x=-1,5+2,5\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}x=3\\x=1\end{cases}}\)

\(\frac{3}{4}+\frac{1}{4}:x=\frac{2}{5}\)                              \(/x-2.5/=1.5\)

\(\frac{1}{4}:x=\frac{2}{5}-\frac{3}{4}\)                            \(\Rightarrow x-2.5=1.5;x-2.5=-1.5\)

\(\frac{1}{4}:x=-\frac{7}{20}\)                                  \(TH1:x-2.5=1.5\Rightarrow x=4\)

\(x=\frac{1}{4}:-\frac{7}{20}\)                                      \(TH2:x-2.5=-1.5\Rightarrow1\)

\(x=-\frac{5}{7}\)                                              

1) \(|5x-3|=|7-x|\)

\(\Leftrightarrow\orbr{\begin{cases}5x-3=7-x\\5x-3=x-7\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}6x=10\\4x=-4\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}x=\frac{5}{3}\\x=-1\end{cases}}\)

Vậy...

2) \(2.|3x-1|-3x=7\)

\(\Leftrightarrow2.|3x-1|=7+3x\)

\(\Leftrightarrow\orbr{\begin{cases}2.\left(3x-1\right)=7+3x\\2.\left(3x-1\right)=-7-3x\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}6x-2=7+3x\\6x-2=-7-3x\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}3x=9\\9x=-5\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}x=3\\x=\frac{-5}{9}\end{cases}}\)

Vậy...

5) \(\text{1,6 - |x + 1,5| = 0}\)

\(|x + 1,5| = 1,6-0\)

\(\text{|x + 1,5| = 1,6}\)

\( |x | = 1,6-1,5\)

\(|x|=0,1\)

a) x-12=-15
x=-15+12
x=-3
b) 123-5(x+4)=38
5(x+4)=123-38
5(x+4)=85
x+4=85:5=17
x=17-4
x=13

\(a.x-12=-15\)                    \(b.123-5.\left(x+4\right)=38\)

\(x=\left(-15\right)+12\)                        \(5.\left(x+4\right)=123-38\)

\(x=-3\)                                      \(5.\left(x+4\right)=85\)           

                                                   \(x+4=85:5=17\)

                                                    \(x=17-4=13\)

a) x-12=-15
x=-15+12
x=-3
b) 123-5(x+4)=38
5(x+4)=123-38
5(x+4)=85
x+4=85:5=17
x=17-4
x=13