Ôn tập toán 6

NT

Tìm x:

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

b) \(\dfrac{1}{2}-\left(\dfrac{2}{3}x-\dfrac{1}{3}\right)=\dfrac{2}{3}\)

H24
6 tháng 6 2017 lúc 8:36

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

\(\Rightarrow\left(\dfrac{9}{2}-2x\right)\cdot\dfrac{4}{3}=\dfrac{4}{3}\)

\(\Leftrightarrow6-\dfrac{8}{3}x=\dfrac{4}{3}\)

\(\Leftrightarrow18-8x=4\)

\(\Leftrightarrow-8x=4-18\)

\(\Leftrightarrow-8x=-14\)

\(\Rightarrow x=\dfrac{7}{4}\)

Vậy \(x=\dfrac{7}{4}\)

b) \(\dfrac{1}{2}-\left(\dfrac{2}{3}x-\dfrac{1}{3}\right)=\dfrac{2}{3}\)

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

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

\(\Leftrightarrow5-4x=4\)

\(\Leftrightarrow-4x=4-5\)

\(\Leftrightarrow-4x=-1\)

\(\Rightarrow x=\dfrac{1}{4}\)

Vậy \(x=\dfrac{1}{4}\)

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PH
6 tháng 6 2017 lúc 8:35

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

\(\left(4,5-2x\right):\dfrac{3}{4}=\dfrac{4}{3}\)

\(4,5-2x=\dfrac{4}{3}.\dfrac{3}{4}\)

\(4,5-2x=1\)

\(2x=4,5-1\)

\(2x=3,5=\dfrac{7}{2}\)

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

\(x=\dfrac{7}{4}\)

b) \(\dfrac{1}{2}-\left(\dfrac{2}{3}x-\dfrac{1}{3}\right)=\dfrac{2}{3}\)

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

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

\(\dfrac{2}{3}x=\dfrac{-1}{6}+\dfrac{1}{3}\)

\(\dfrac{2}{3}x=\dfrac{1}{6}\)

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

\(x=\dfrac{1}{4}\)

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MS
6 tháng 6 2017 lúc 8:33

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

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

4,5-2x=\(\dfrac{4}{3}.\dfrac{3}{4}\)

4,5-2x=1

2x=4,5-1

2x=3,5

x=3,5:2

x=\(\dfrac{7}{4}\)

b)\(1\left(\dfrac{2}{3}x-\dfrac{1}{3}\right)=\dfrac{2}{3}\)

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

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

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

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

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

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TM
6 tháng 6 2017 lúc 8:35

a, \(\left(4,5-2x\right)\div\dfrac{3}{4}=1\dfrac{1}{3}\)

\(\dfrac{9}{2}-2x=\dfrac{4}{3}.\dfrac{3}{4}\)

\(\dfrac{9}{2}-2x=1\Rightarrow2x=\dfrac{9}{2}-1\)

\(\Rightarrow2x=\dfrac{7}{2}\Rightarrow x=\dfrac{7}{2}\div2=\dfrac{7}{4}\)

Vậy x = \(\dfrac{7}{4}\)

b, \(\dfrac{1}{2}-\left(\dfrac{2}{3}x-\dfrac{1}{3}\right)=\dfrac{2}{3}\)

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

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

\(\dfrac{2}{3}x=\dfrac{-1}{6}+\dfrac{1}{3}\Rightarrow\dfrac{2}{3}x=\dfrac{1}{6}\)

\(x=\dfrac{1}{6}\div\dfrac{2}{3}=\dfrac{1}{6}.\dfrac{3}{2}=\dfrac{1}{4}\)

Vậy \(x=\dfrac{1}{4}\)

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