Question

[Gia Huy To]

 giúp mik bài này cảm ơn ạ

Answer 1

[HT.Phong (9A5)]

Bài 2:

a) \(\dfrac{5}{6}:x=\dfrac{13}{9}\cdot\dfrac{3}{26}\)

\(\Rightarrow\dfrac{5}{6}:x=\dfrac{3}{9\cdot2}\)

\(\Rightarrow\dfrac{5}{6}:x=\dfrac{1}{6}\)

\(\Rightarrow x=\dfrac{5}{6}:\dfrac{1}{6}\)

\(\Rightarrow x=5\) 

b) \(\dfrac{x-1}{21}=\dfrac{3}{x+1}\)

\(\Rightarrow\left(x-1\right)\left(x+1\right)=3\cdot21\)

\(\Rightarrow x^2-x+x-1=63\)

\(\Rightarrow x^2-1=63\)

\(\Rightarrow x^2-64=0\)

\(\Rightarrow x^2-8x+8x-64=0\)

\(\Rightarrow x\left(x-8\right)+8\left(x-8\right)=0\)

\(\Rightarrow\left(x+8\right)\left(x-8\right)=0\)

TH1: `x+8=0=>x=-8`

TH2: `x-8=0=>x=8` 

c) \(2\dfrac{1}{2}x+x=2\dfrac{1}{17}\)

\(\Rightarrow\dfrac{5}{2}x+x=\dfrac{35}{17}\)

\(\Rightarrow x\cdot\left(\dfrac{5}{2}+1\right)=\dfrac{35}{17}\)

\(\Rightarrow x\cdot\dfrac{7}{2}=\dfrac{35}{17}\)

\(\Rightarrow x=\dfrac{35}{17}:\dfrac{7}{2}\)

\(\Rightarrow x=\dfrac{10}{17}\)
d) \(x-3\dfrac{1}{2}x=-2\dfrac{6}{7}\)

\(\Rightarrow x-\dfrac{7}{2}x=-\dfrac{20}{7}\)

\(\Rightarrow x\cdot\left(1-\dfrac{7}{2}\right)=\dfrac{-20}{7}\)

\(\Rightarrow x\cdot\dfrac{-5}{2}=\dfrac{-20}{7}\)

\(\Rightarrow x=\dfrac{-20}{7}:\dfrac{-5}{2}\)

\(\Rightarrow x=\dfrac{8}{7}\) 

Answer 2

[Nguyễn Lê Phước Thịnh]

Bài 2:

a: \(\dfrac{5}{6}:x=\dfrac{13}{9}\cdot\dfrac{3}{26}\)

=>\(\dfrac{5}{6}:x=\dfrac{13}{26}\cdot\dfrac{3}{9}=\dfrac{1}{6}\)

=>\(x=\dfrac{5}{6}:\dfrac{1}{6}=\dfrac{5}{6}\cdot\dfrac{6}{1}=5\)

b: 

ĐKXĐ: x<>-1

\(\dfrac{x-1}{21}=\dfrac{3}{x+1}\)

=>\(\left(x-1\right)\left(x+1\right)=3\cdot21\)

=>\(x^2-1=63\)

=>\(x^2=64\)

=>\(\left[{}\begin{matrix}x=8\left(nhận\right)\\x=-8\left(nhận\right)\end{matrix}\right.\)

c: \(2\dfrac{1}{2}\cdot x+x=2\dfrac{1}{17}\)

=>\(x\left(2,5+1\right)=\dfrac{35}{17}\)

=>\(x\cdot\dfrac{7}{2}=\dfrac{35}{17}\)

=>\(x=\dfrac{35}{17}:\dfrac{7}{2}=\dfrac{35}{17}\cdot\dfrac{2}{7}=\dfrac{10}{17}\)

d: \(x-3\dfrac{1}{2}x=-2\dfrac{6}{7}\)

=>\(x\left(1-3,5\right)=-\dfrac{20}{7}\)

=>\(x\cdot2,5=\dfrac{20}{7}\)

=>\(x=\dfrac{8}{7}\)