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a, 89 - (73 - \(x\)) = 20
73 - \(x\) = 89 - 20
73 - \(x\) = 69
\(x\) = 73 - 69
\(x\) = 4
b, 7\(x\) - 2\(x\) = 617:615 + 44:11
5\(x\) = 62 + 4
5\(x\) = 36 + 4
5\(x\) = 40
\(x\) = 40: 5
\(x\) = 8
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2+4+6+8+...+2x=210
+) Ta có : 2.1+2.2+2.3+2.4+...+2x=210
=>2.(1+2+3+...x) =210
1+2+3+...+x= 210:2
1+2+3+...+x= 105
(x+1).x:2=105 =>(x+1).x=210 =>15.14=210
+) Vậy x=14
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\(\frac{6}{11}\cdot\frac{3}{14}+\frac{-5}{16}+\frac{3}{14}\cdot\frac{5}{11}+\frac{-3}{16}\)
\(=\frac{6}{11}\cdot\frac{3}{14}+\frac{3}{14}\cdot\frac{5}{11}+\frac{-5}{16}+\frac{-3}{16}\)
\(=\frac{3}{14}\cdot\left(\frac{6}{11}+\frac{5}{11}\right)+\left(\frac{-5}{16}+\frac{-3}{16}\right)\)
\(=\frac{3}{14}\cdot\frac{6+5}{11}+\frac{-5+\left(-3\right)}{16}\)
\(=\frac{3}{14}\cdot\frac{11}{11}+\frac{-8}{16}\)
\(=\frac{3}{14}\cdot1+\frac{-1}{2}\)
\(=\frac{3}{14}+\frac{-1}{2}\)
\(=\frac{3}{14}+\frac{-7}{14}\)
\(=\frac{3+\left(-7\right)}{14}\)\(=\frac{-4}{14}=\frac{-2}{7}\)
\(\frac{-5}{6}+\left(7x-\frac{1}{2}\right)\cdot\frac{2}{9}=-1\frac{1}{3}\)
\(\frac{-5}{6}+\frac{14}{9}\cdot x-\frac{1}{9}=-\frac{4}{3}\)
\(\frac{14}{9}\cdot x-\frac{1}{9}=-\frac{4}{3}+\frac{5}{6}\)
\(\frac{14}{9}\cdot x-\frac{1}{9}=-\frac{1}{2}\)
\(\frac{14}{9}\cdot x=-\frac{1}{2}+\frac{1}{9}\)
\(\frac{14}{9}\cdot x=-\frac{7}{18}\)
\(x=-\frac{7}{18}:\frac{14}{9}\)
\(x=-\frac{1}{4}\)
`(2x-6)^3=8`
`(2x-6)^3=2^3`
`2x-6=2`
`2x =2+6=8`
`x=8/2=4`
(2x-6)^3=8
(2x-6)^3=2^3
2x-6=2
2x=8
x=4.
Vâỵ x= 4.