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\(\Rightarrow\dfrac{5}{4}-\dfrac{1}{4}x=\dfrac{3}{10}x-\dfrac{2}{5}\)
\(\Rightarrow\dfrac{5}{4}+\dfrac{2}{5}=\dfrac{3}{10}x-\dfrac{1}{4}x\)
\(\Rightarrow\dfrac{33}{20}=\dfrac{11}{20}x\)
\(\Rightarrow x=\dfrac{33}{20}\div\dfrac{11}{20}\)
\(\Rightarrow x=3\)
\(1\dfrac{1}{4}-x\dfrac{1}{4}=x\cdot30\%\cdot\dfrac{2}{5}\)
\(\Leftrightarrow\dfrac{5}{4}-x\dfrac{1}{4}=x\cdot\dfrac{3}{10}-\dfrac{2}{5}\)
\(\Leftrightarrow\dfrac{5}{4}-\dfrac{1}{4}x=\dfrac{3}{10}x-\dfrac{2}{5}\)
\(\Leftrightarrow25-5x=6x-8\)
\(\Leftrightarrow-5x-6x=-8-25\)
\(\Leftrightarrow-11x=-33\)
\(\Leftrightarrow x=3\)
Vậy x = 3
a, \((\dfrac{-1}{2})\)2 -\(\dfrac{5}{6}\).\((\dfrac{-6}{7})-\dfrac{3}{4}:1\dfrac{2}{3}\)
=\(\dfrac{1}{4}+\dfrac{5}{7}-\dfrac{9}{20}\)
=\(\dfrac{35}{140}+\dfrac{100}{140}-\dfrac{63}{140}\)
=\(\dfrac{72}{140}\)= \(\dfrac{18}{35}\)
\(\left(4x-3\right)\left(\dfrac{3}{5}x+\dfrac{1}{2}\right)=0\)
\(=>4x-3=0\) hoặc \(\dfrac{3}{5}x+\dfrac{1}{2}=0\)
\(=>x=\dfrac{3}{4}\) hoặc x = -5/6
(4x - 3).(\(\dfrac{3}{5}\)x + \(\dfrac{1}{2}\)) = 0
=> TH1: 4x - 3 = 0
=> 4x =3
=> x = loại
=>TH2: (\(\dfrac{3}{5}\)x + \(\dfrac{1}{2}\)) = 0
=> \(\dfrac{3}{5}\) x = \(\dfrac{1}{2}\)
=> x = \(\dfrac{1}{2}\): \(\dfrac{3}{5}\)
=> x = \(\dfrac{5}{6}\)
Ta có :
\(\left(3n+2\right)^4=\left(3n+2\right)^6\)
\(\Leftrightarrow\left(3n+2\right)^6-\left(3n+2\right)^4=0\)
\(\Leftrightarrow\left[\left(3n+2\right)^2-1\right]-\left(3n+4\right)^4=0\)
\(\Leftrightarrow\left\{{}\begin{matrix}\left[\left(3n+2\right)^2-1\right]=0\\\left(3n+2\right)^4=0\end{matrix}\right.\)
+)\(\left(3n+2\right)^4=0\)
\(\Leftrightarrow n=\dfrac{2}{3}\)\(\left(tm\right)\)
+) \(\left[\left(3n+2\right)^2-1\right]=0\)
\(\Leftrightarrow\left\{{}\begin{matrix}3n+2=1\\3n+2=-1\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}n=\dfrac{-1}{3}\\n=-1\end{matrix}\right.\)\(\left(tm\right)\)
Vậy ....................
Đo thanh gỗ có chiều dài \(:L\)
Nối sợi dây tới điểm có độ dài : \(\dfrac{L}{2}\)
=> Ta chia được thanh gỗ thành 2 phần bắng nhau
\(\left[\left(6x-72\right):2-84\right].28=5628\)
\(\Leftrightarrow\left(6x-72\right):2-84=5628:28\)
\(\Leftrightarrow\left(6x-72\right):2-84=201\)
\(\Leftrightarrow\left(6x-72\right):2=201+84\)
\(\Leftrightarrow\left(6x-72\right):2=285\)
\(\Leftrightarrow6x-72=285.2\)
\(\Leftrightarrow6x-72=570\)
\(\Leftrightarrow6x=570+72\)
\(\Leftrightarrow6x=642\)
\(\Leftrightarrow x=642:6\)
\(\Leftrightarrow x=107\)
Vậy \(x=107\)
[(6.x-72):2-84].28=5628
(6.x-72):2-84=5628:28=201
(6.x-72):2=201+84=285
6.x-72=285*2=570
6.x=570+72=642
x=642:6=107
Vậy x = 107
B7 chu vi mảnh vườn là 3,3 m
diện tích là \(\dfrac{8}{7}\)m vuông
Bài 7:
Chu vi là:
\(\left(\dfrac{12}{5}+\dfrac{10}{21}\right)\cdot2=\dfrac{604}{105}\left(m\right)\)
Diện tích là:
\(\dfrac{12}{5}\cdot\dfrac{10}{21}=\dfrac{8}{7}\left(m^2\right)\)