Question

2. Tìm x, biết

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

b) 2x.(x -\(\dfrac{1}{7}\))=0

Giúp mình với

Answer 1

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

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

\(\Leftrightarrow x=\dfrac{1}{4}:\dfrac{-7}{20}=-\dfrac{1}{4}.\dfrac{20}{7}=\dfrac{-5}{7}\)

b)\(2x\left(x-\dfrac{1}{7}\right)=0\)

\(\Leftrightarrow\left\{{}\begin{matrix}2x=0\\x-\dfrac{1}{7}=0\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x=0\\x=\dfrac{1}{7}\end{matrix}\right.\)

Answer 2

\(\dfrac{3}{4}+\dfrac{1}{4}:x=\dfrac{2}{5}\)

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

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

\(\Leftrightarrow x=\dfrac{1}{4}:\dfrac{-7}{20}=\dfrac{5}{-7}\)
\(2x\left(x-\dfrac{1}{7}\right)=0\)

\(\Leftrightarrow2x=0\Rightarrow x=0\)

\(\Leftrightarrow x-\dfrac{1}{7}=0\Rightarrow x=\dfrac{1}{7}\)

Answer 3

b, 2x.(x-\(\dfrac{1}{7}\) )=0

x(2-\(\dfrac{1}{7}\))=0

x.\(\dfrac{13}{7}\)=0

x=0:\(\dfrac{13}{7}\)

x=0

Vậy x=0

Answer 4

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

\(\Rightarrow\dfrac{1}{4}:x=\dfrac{2}{5}-\dfrac{3}{4}\)

\(\Rightarrow\dfrac{1}{4}:x=-\dfrac{7}{20}\)

\(\Rightarrow x=\dfrac{1}{4}:\left(-\dfrac{7}{20}\right)\)

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

b) \(2x\left(x-\dfrac{1}{7}\right)\)

\(\Rightarrow\left[{}\begin{matrix}2x=0\\x-\dfrac{1}{7}=0\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x=0:2\\x=0+\dfrac{1}{7}\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x=0\\x=\dfrac{1}{7}\end{matrix}\right.\)

Answer 5

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

=> \(\dfrac{1}{4}:x=\dfrac{2}{5}-\dfrac{3}{4}\)

=>\(\dfrac{1}{4}:x=\dfrac{-7}{20}\)

=> x = \(\dfrac{1}{4}:\dfrac{-7}{20}\)

=> x = \(\dfrac{-5}{7}\)

Answer 6

b, 2x.(x- \(\dfrac{1}{7}\))=0

hoặc 2x =0 => x = 0:2 =>x =0

hoặc x-\(\dfrac{1}{7}\)=0 => x =\(\dfrac{1}{7}\)

Vậy x \(\in\)\(\left\{0;\dfrac{1}{7}\right\}\)