Đại số lớp 6

VH

Tìm x

a) \(\left|1-x\right|=\dfrac{1}{4}\)

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

c) \(\dfrac{2x}{3}-\dfrac{x}{4}=\dfrac{5}{6}\)

H24
25 tháng 4 2017 lúc 20:51

a) \(\left|1-x\right|=\dfrac{1}{4}\)

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

Vậy: \(x=\dfrac{3}{4};\dfrac{5}{4}\)

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

\(\Leftrightarrow2\left(x+1\right)=3x\)

\(\Leftrightarrow2x+2=3x\)

\(\Leftrightarrow2x-3x=-2\)

\(\Leftrightarrow-x=-2\)

\(\Leftrightarrow x=2\)

Vậy: \(x=2\)

c) \(\dfrac{2x}{3}-\dfrac{x}{4}=\dfrac{5}{6}\)

\(\Leftrightarrow8x-3x=10\)

\(\Leftrightarrow5x=10\)

\(\Leftrightarrow x=2\)

Vậy: \(x=2\)

Bình luận (0)
HN
25 tháng 4 2017 lúc 20:53

a) Ta có: \(\left|1-x\right|=\dfrac{1}{4}\)

\(\Rightarrow\left[{}\begin{matrix}1-x=\dfrac{1}{4}\\1-x=-\dfrac{1}{4}\end{matrix}\right.\) \(\Rightarrow\left[{}\begin{matrix}x=1-\dfrac{1}{4}\\x=1-\left(-\dfrac{1}{4}\right)\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x=\dfrac{3}{4}\\x=\dfrac{5}{4}\end{matrix}\right.\)

b) Vì \(\dfrac{x+1}{3}=\dfrac{x}{2}\Leftrightarrow2\left(x+1\right)=3x\)

\(\Leftrightarrow2x+2=3x\)

\(\Leftrightarrow x=3x-2x\)

\(\Leftrightarrow x=2\)

c) Ta có: \(\dfrac{2x}{3}-\dfrac{x}{4}=\dfrac{5}{6}\)

\(\Rightarrow\dfrac{8x}{12}-\dfrac{3x}{12}=\dfrac{10}{12}\)

\(\Rightarrow\dfrac{8x-3x}{12}=\dfrac{10}{12}\)

\(\Rightarrow\dfrac{x\left(8-3\right)}{12}=\dfrac{10}{12}\)

\(\Rightarrow\dfrac{5x}{12}=\dfrac{10}{12}\Rightarrow5x=10\Rightarrow x=2\)

Vậy \(x=2\)

Bình luận (1)

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