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{ [ ( 1 + 2 ) x 3 - 4 ] : 5 + 6 }x7^8
= { [ 3 x 3 - 4 ] : 5 + 6 }
= { [ 9 - 4 ] : 5 + 6 }
= { 5 : 5 + 6 }
= { 1 + 6 }
= 7
KẾT BẠN NHA
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\(\frac{1}{1\cdot3}+\frac{1}{3\cdot5}+\frac{1}{5\cdot7}+...+\frac{1}{2009\cdot2011}\)
\(=\frac{3-1}{1\cdot3}+\frac{5-3}{3\cdot5}+\frac{7-5}{5\cdot7}+...+\frac{2011-2009}{2009\cdot2011}\)
\(=\frac{2}{1\cdot3}+\frac{2}{3\cdot5}+\frac{2}{5\cdot7}+....+\frac{2}{2009\cdot2011}\)
\(=\frac{1}{2}\cdot\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{2009}-\frac{1}{2011}\right)\)
\(=\frac{1}{2}\cdot\left(1-\frac{1}{2011}\right)\)
\(=\frac{1}{2}\cdot\frac{2010}{2011}=\frac{1005}{2011}\)
Đặt \(A=\frac{1}{1\times3}+\frac{1}{3\times5}+\frac{1}{5\times7}+...+\frac{1}{2009\times2011}\)
\(2A=\frac{2}{1\times3}+\frac{2}{3\times5}+\frac{2}{5\times7}+...+\frac{2}{2009\times2011}\)
\(2A=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{2009}-\frac{1}{2011}\)
\(2A=1-\frac{1}{2011}=\frac{2010}{2011}\Rightarrow A=\frac{1005}{2011}\)
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( 4x + 5 ) : 3 - 121 : 11 = 14
=) (4x + 5) : 3 - 11 = 14
=) (4x +5) : 3 = 25
=) 4x + 5 = 75
=) 4x = 80
=) x = 20
Vậy x = 20
Chúc bạn học tốt =))
( 4x + 5 ) : 3 - 121 : 11 = 14
( 4x + 5 ) : 3 - 11 = 14
( 4x + 5 3 = 14 + 11
( 4x + 5 ) : 3 = 25
4x + 5 = 25 x 3
4x + 5 = 75
4x = 75 - 5
4x = 70
x = 70 : 4
x = 17,5
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\(Ư\left(4\right)\in\left\{1;-1;2;-2;4;-4\right\}\)
\(Ư\left(6\right)\in\left\{1;-1;2;-2;3;-3;6;-6\right\}\)
\(Ư\left(9\right)\in\left\{1;-1;3;-3;9;-9\right\}\)
\(Ư\left(13\right)\in\left\{1;-1;13;-13\right\}\)
\(Ư\left(1\right)\in\left\{1;-1\right\}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{-3}{-9}\)+\(\frac{8}{7}\)+\(\frac{1}{-3}\)+\(\frac{26}{14}\)
=+\(\frac{8}{7}\)+\(\frac{1}{-3}\)+\(\frac{13}{7}\)
=\(\frac{1}{3}\)+\(\frac{1}{-3}\)+\(\frac{8}{7}\)+\(\frac{13}{7}\)
=0+\(\frac{8}{7}\)+\(\frac{13}{7}\)
=\(\frac{21}{7}\)
=3
Đáp án của bạn là x=1 nha bạn.
3x+5=8
3x=8-5
3x=3
x=3:3
x=1