Tách ra từng câu rồi đăng thành câu hỏi nhé

Bài 3: 

a: \(x=\dfrac{1}{4}-\dfrac{2}{13}=\dfrac{13}{52}-\dfrac{8}{52}=\dfrac{5}{52}\)

b: \(\dfrac{x}{3}=\dfrac{2}{3}-\dfrac{1}{7}\)

nên \(x\cdot\dfrac{1}{3}=\dfrac{14}{21}-\dfrac{3}{21}=\dfrac{11}{21}\)

hay \(x=\dfrac{11}{21}:\dfrac{1}{3}=\dfrac{11}{7}\)

8. a)(231-39)-231=39-(231-231)=39-0=39

Bài 11: 

a: =x+51-56+24=x+19

b: =-65-x-27+26=-x-56

=-5

-5

(x-2)³=216

=>\(\left(x-2\right)^3=6^3\)

=>x-2=6

=>x=8

x=8

a: =14/13-1/13-19/20=1-19/20=1/20

b: =-24/17+7/17+1/16=-1+1/16=-15/16

\(\left(2x-15\right)^5=\left(2x-15\right)^3\)

\(\Rightarrow\left(2x-15\right)^5-\left(2x-15\right)^3=0\)

\(\Rightarrow\left(2x-15\right)^3\left[\left(2x-15\right)^2-1\right]=0\)

\(\Rightarrow\left(2x-15\right)^3\left(2x-15-1\right)\left(2x-15+1\right)=0\)

\(\Rightarrow\left(2x-15\right)^3\left(2x-16\right)\left(2x-14\right)=0\)

\(\Rightarrow\left[{}\begin{matrix}2x-15=0\\2x-16=0\\2x-14=0\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}2x=15\\2x=16\\2x=14\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x=\dfrac{15}{2}\\x=8\\x=7\end{matrix}\right.\)

tròi ơi hay v 

a: =-5/6-3/7=-35/42-18/42=-53/42

b: =2/5-4/9=18/45-20/45=-2/45

c: =-24/35

d: =2/3x-5/4=-10/12=-5/6

\((-12).36 - 12.64 =-432 - 768 =-1200\)

\(\dfrac{3}{x+2}\)=\(\dfrac{5}{2x+1}\)(x khác -1/2 và x khác -2)

=>6x+3=5x+10

<=>x=7 tm