Ôn tập toán 6

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Vy Nguyễn

Tìm x. ( giúp mình với, ra lâu rồi không ai làm khocroi )

e) \(\dfrac{-2}{3}-\dfrac{1}{3}\left(2x-5\right)=\dfrac{3}{2}\)

g) \(\dfrac{2}{5}.x+\dfrac{1}{2}=\dfrac{-3}{4}\)

h) \(\left(2x-2\dfrac{4}{5}\right):3\dfrac{1}{8}=1\dfrac{3}{5}\)

i) \(3,2x-\left(\dfrac{4}{5}+\dfrac{2}{3}\right):3\dfrac{2}{3}=\dfrac{7}{20}\)

k)\(\left(\dfrac{3x}{7}+1\right):\left(-4\right)=\dfrac{-1}{28}\)

Làm giúp mình với, mình hứa tick cho!~bucminh

Nam Nguyễn
16 tháng 4 2017 lúc 20:59

ừ Vy Nguyễn, mik làm nè:

e, \(\dfrac{-2}{3}-\dfrac{1}{3}\left(2x-5\right)=\dfrac{3}{2}.\)

\(\dfrac{1}{3}\left(2x-5\right)=\dfrac{-2}{3}-\dfrac{3}{2}.\)

\(\dfrac{1}{3}\left(2x-5\right)=\dfrac{-4}{6}+\dfrac{-9}{6}.\)

\(\dfrac{1}{3}\left(2x-5\right)=\dfrac{-13}{6}.\)

\(2x-5=\dfrac{-13}{6}:\dfrac{1}{3}.\)

\(2x-5=\dfrac{-13}{6}.3.\)

\(2x-5=\dfrac{-13}{2}.\)

\(2x=\dfrac{-13}{2}+5.\)

\(2x=\dfrac{-13}{2}+\dfrac{10}{2}.\)

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

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

\(x=\dfrac{-3}{2.2}=\dfrac{-3}{4}.\)

g, \(\dfrac{2}{5}x+\dfrac{1}{2}=\dfrac{-3}{4}.\)

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

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

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

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

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

\(x=\dfrac{-25}{8}.\)

h, \(\left(2x-2\dfrac{4}{5}\right):3\dfrac{1}{8}=1\dfrac{3}{5}.\)

\(\left(2x-2\dfrac{4}{5}\right)=\dfrac{8}{5}.\dfrac{25}{8}.\)

\(\left(2x-2\dfrac{4}{5}\right)=5.\)

\(2x=5+2\dfrac{4}{5}.\)

\(2x=7\dfrac{4}{5}.\)

\(x=7\dfrac{4}{5}:2.\)

\(x=\dfrac{39}{10}.\)

(còn tiếp ở phần sau!!!)

Nam Nguyễn
16 tháng 4 2017 lúc 21:25

Tiếp:

i, \(3,2x-\left(\dfrac{4}{5}+\dfrac{2}{3}\right):3\dfrac{2}{3}=\dfrac{7}{20}.\)

\(\dfrac{16}{5}x-\left(\dfrac{4}{5}+\dfrac{2}{3}\right)=\dfrac{7}{20}.\dfrac{11}{3}.\)

\(\dfrac{16}{5}x-\left(\dfrac{4}{5}+\dfrac{2}{3}\right)=\dfrac{77}{60}.\)

\(\dfrac{16}{5}x-\left(\dfrac{12}{15}+\dfrac{10}{15}\right)=\dfrac{77}{60}.\)

\(\dfrac{16}{5}x-\dfrac{22}{15}=\dfrac{77}{60}.\)

\(\dfrac{16}{5}x=\dfrac{77}{60}+\dfrac{22}{15}.\)

\(\dfrac{16}{5}x=\dfrac{77}{60}+\dfrac{88}{60}.\)

\(\dfrac{16}{5}x=\dfrac{165}{60}=\dfrac{11}{4}.\)

\(x=\dfrac{11}{4}:\dfrac{16}{5}.\)

\(x=\dfrac{11}{4}.\dfrac{5}{16}=\dfrac{55}{64}.\)

k, \(\left(\dfrac{3x}{7}+1\right):\left(-4\right)=\dfrac{-1}{28}.\)

\(\left(\dfrac{3x}{7}+1\right)=\dfrac{-1}{28}.\left(-4\right).\)

\(\left(\dfrac{3x}{7}+1\right)=\dfrac{1}{7}.\)

\(\dfrac{3x}{7}=\dfrac{1}{7}-1.\)

\(\dfrac{3x}{7}=\dfrac{1}{7}-\dfrac{7}{7}.\)

\(\dfrac{3x}{7}=\dfrac{-6}{7}.\)

\(\Rightarrow3x=-6.\)

\(\Rightarrow x=-6:3=-2.\)

~ Chúc bn học tốt!!! ~

Bài mik đúng thì nhớ tik mik nha!!!

Sáng
16 tháng 4 2017 lúc 20:01

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

\(\Rightarrow\dfrac{1}{3}\left(2x-5\right)=\dfrac{-2}{3}+\dfrac{3}{2}\)

\(\Rightarrow\dfrac{1}{3}\left(2x-5\right)=\dfrac{-5}{6}\)

\(\Rightarrow2x-5=\dfrac{-5}{6}.3\)

\(\Rightarrow2x-5=\dfrac{-5}{2}\)

\(\Rightarrow2x=\dfrac{5}{2}\)

\(\Rightarrow x=\dfrac{5}{2}.\dfrac{1}{2}\)

\(\Rightarrow x=\dfrac{5}{4}\)

b, \(\dfrac{2}{5}x+\dfrac{1}{2}=\dfrac{-3}{4}\)

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

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

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

\(\Rightarrow x=\dfrac{-5}{8}\)

c, \(\left(2x-2\dfrac{4}{5}\right):3\dfrac{1}{8}=1\dfrac{3}{5}\)

\(\Rightarrow\left(2x-\dfrac{14}{5}\right):\dfrac{25}{8}=\dfrac{8}{5}\)

\(\Rightarrow2x-\dfrac{14}{5}=\dfrac{8}{5}.\dfrac{25}{8}\)

\(\Rightarrow2x-\dfrac{14}{5}=5\)

\(\Rightarrow2x=5+\dfrac{14}{5}\)

\(\Rightarrow2x=\dfrac{39}{5}\)

\(\Rightarrow x=\dfrac{39}{5}.\dfrac{1}{2}\)

\(\Rightarrow x=\dfrac{39}{10}\)

d, \(3,2x-\left(\dfrac{4}{5}+\dfrac{2}{3}\right):3\dfrac{2}{3}=\dfrac{7}{20}\)

\(\Rightarrow\dfrac{16}{5}x-\dfrac{22}{15}:\dfrac{11}{3}=\dfrac{7}{20}\)

\(\Rightarrow\dfrac{16}{5}x-\dfrac{3}{5}=\dfrac{7}{20}\)

\(\Rightarrow\dfrac{16}{5}x=\dfrac{7}{20}+\dfrac{3}{5}\)

\(\Rightarrow\dfrac{16}{5}x=\dfrac{19}{20}\)

\(\Rightarrow x=\dfrac{19}{20}.\dfrac{5}{16}\)

\(\Rightarrow x=\dfrac{19}{64}\)

e, \(\left(\dfrac{3x}{7}+1\right):\left(-4\right)=\dfrac{-1}{28}\)

\(\Rightarrow\dfrac{3x}{7}+1=\dfrac{-1}{28}.\left(-4\right)\)

\(\Rightarrow\dfrac{3x}{7}+1=\dfrac{1}{7}\)

\(\Rightarrow\dfrac{3x}{7}=\dfrac{1}{7}-1\)

\(\Rightarrow\dfrac{3x}{7}=\dfrac{-6}{7}\)

\(\Rightarrow3x=-6\)

\(\Rightarrow x=-2\)


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