a, X x 3 và 1/3 = 3 và 1/3 :4 và 1/4
b, 5 và 2/3 : X = 3 và 2/3 - 2 và 1/2
c, X x 3,9 + X x 0.1 = 2,7
giúp mk với akkk
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Bài 1
a) 3 2/5 - 1/2
= 17/5 - 1/2
= 34/10 - 5/10
= 29/10
b) 4/5 + 1/5 × 3/4
= 4/5 + 3/20
= 16/20 + 3/20
= 19/20
c) 3 1/2 × 1 1/7
= 7/2 × 8/7
= 4
d) 4 1/6 : 2 1/3
= 25/6 : 7/3
= 25/14
Bài 2
a) 3 × 1/2 + 1/4 × 1/3
= 3/2 + 1/12
= 18/12 + 1/12
= 19/12
b) 1 4/5 - 2/3 : 2 1/3
= 9/5 - 2/3 : 7/3
= 9/5 - 2/7
= 63/35 - 10/35
= 53/35
\(1,\left(3x+2\right)\left(5-x^2\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}3x+2=0\\5-x^2=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{2}{3}\\-x^2=-5\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{2}{3}\\x=\pm\sqrt{5}\end{matrix}\right.\)
Vậy \(S=\left\{-\dfrac{2}{3};-\sqrt{5};\sqrt{5}\right\}\)
\(2,-2x-\dfrac{2}{3}\left(\dfrac{3}{4}-\dfrac{1}{8}x\right)=\left(-\dfrac{1}{2}\right)^3\)
\(\Leftrightarrow-2x-\dfrac{1}{2}+\dfrac{1}{12}x=-\dfrac{1}{8}\)
\(\Leftrightarrow-2x+\dfrac{1}{12}x=-\dfrac{1}{8}+\dfrac{1}{2}\)
\(\Leftrightarrow-\dfrac{23}{12}=\dfrac{3}{8}\)
\(\Leftrightarrow x=-\dfrac{9}{46}\)
Vậy \(S=\left\{-\dfrac{9}{46}\right\}\)
\(3,\dfrac{1}{12}:\dfrac{4}{21}=3\dfrac{1}{2}:\left(3x-2\right)\)
\(\Leftrightarrow\dfrac{1}{12}.\dfrac{21}{4}=\dfrac{7}{2}.\dfrac{1}{3x-2}\)
\(\Leftrightarrow\dfrac{7}{16}=\dfrac{7}{6x-4}\)
\(\Leftrightarrow6x-4=7:\dfrac{7}{16}\)
\(\Leftrightarrow6x-4=16\)
\(\Leftrightarrow x=\dfrac{10}{3}\)
Vậy \(S=\left\{\dfrac{10}{3}\right\}\)
\(4,\dfrac{x-1}{x+2}=\dfrac{4}{5}\left(dk:x\ne-2\right)\)
\(\Rightarrow5\left(x-1\right)=4\left(x+2\right)\)
\(\Rightarrow5x-5=4x+8\)
\(\Rightarrow x=13\left(tmdk\right)\)
Vậy \(S=\left\{13\right\}\)
a) \(x.\frac{3}{4}=\frac{4}{5}.2\)
\(x.\frac{3}{4}=\frac{8}{5}\)
\(x=\frac{8}{5}:\frac{3}{4}=\frac{32}{15}\)
b) \(x:1\frac{1}{7}=2\frac{2}{3}\)
\(x:\frac{8}{7}=\frac{8}{3}\)
\(x=\frac{8}{3}.\frac{8}{7}=\frac{64}{21}\)
c) \(x-1\frac{2}{5}=4\frac{1}{6}-2\frac{2}{3}\)
\(x-\frac{7}{5}=\frac{25}{6}-\frac{8}{3}=\frac{3}{2}\)
\(x=\frac{3}{2}+\frac{7}{5}=\frac{29}{10}\)
d) \(2\frac{2}{3}+x:\frac{3}{2}=2\frac{1}{3}\)
\(\frac{8}{3}+x:\frac{3}{2}=\frac{7}{3}\)vô lí vì 8/3 lớn hơn 7/3
=1,4 x\(\dfrac{15}{49}-\) \(\left(\dfrac{4}{5}+\dfrac{2}{3}\right)\) : 2\(\dfrac{1}{5}\)
= \(\dfrac{3}{7}\) - \(\dfrac{22}{15}\) : \(\dfrac{11}{5}\)
= \(\dfrac{3}{7}\) - \(\dfrac{2}{3}\)
= \(-\dfrac{5}{21}\)
( 2\(\dfrac{1}{5}\) + \(\dfrac{3}{5}\) \(\times\) \(x\)) = \(\dfrac{3}{4}\)
\(\dfrac{11}{5}\) + \(\dfrac{3}{5}\)\(x\) = \(\dfrac{3}{4}\)
\(\dfrac{3}{5}\)\(x\) = \(\dfrac{3}{4}\) - \(\dfrac{11}{5}\)
\(\dfrac{3}{5}\)\(x\) = - \(\dfrac{29}{20}\)
\(x\) = -\(\dfrac{29}{12}\)
a) X x 3 và 1/3 = 3 và 1/3 :4 và 1/4
=> X x 10/3 = 10/3 : 17/4
=> X = 10/3 : 17/4 : 10/3
=> X = ( 10/3 : 10/3 ) ; 17/4
=> X = 1 : 17/4 = 4/17
Vậy X = 4/17
b) 5 và 2/3 : X = 3 và 2/3 - 2 và 1/2
=> 17/3 : X = 11/3 - 5/2
=> 17/3 : X = 7/6
=> X = 17/3 : 7/6 = 34/7
Vậy x = 34/7
c) X x 3,9 + X x 0.1 = 2,7
=> X x ( 3,9 + 0,1 ) = 2,7
=> X x 4 = 2,7
=> X = 2,7 : 4
=> X = 0,675
Vậy x = 0,675