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\(\frac{1}{1.4}+\frac{1}{4.7}+\frac{1}{7.10}+...+\frac{1}{40.43}+\frac{1}{43.46}\)
\(=3.\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{43}-\frac{1}{46}\right)\)
\(=3.\left(1-\frac{1}{46}\right)\)
\(=3.\frac{45}{46}\)
\(=\frac{135}{46}\)
~Học tốt~
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a; \(\dfrac{x-1}{12}\) = \(\dfrac{5}{3}\)
\(x-1\) = \(\dfrac{5}{3}\) \(\times\) 12
\(x\) - 1 = 20
\(x\) = 20 + 1
\(x\) = 21
b; \(\dfrac{-x}{8}\) = \(\dfrac{-50}{x}\)
-\(x\).\(x\) = -50.8
-\(x^2\) = -400
\(x^2\) = 400
\(\left[{}\begin{matrix}x=-20\\x=20\end{matrix}\right.\)
Vậy \(x\) \(\in\) {-20; 20}
c; \(\dfrac{x}{3}\) = \(\dfrac{14}{x+1}\)
\(x\).(\(x\)+1) = 14.3
\(x^2\) + \(x\) = 42
\(x^2\) + \(x\) - 42 = 0
\(x^2\) - 6\(x\) + 7\(x\) - 42 = 0
\(x\).(\(x\) - 6) + 7.(\(x\) - 6) = 0
(\(x\) - 6).(\(x\) + 7) = 0
\(\left[{}\begin{matrix}x-6=0\\x+7=0\end{matrix}\right.\)
\(\left[{}\begin{matrix}x=6\\x=-7\end{matrix}\right.\)
Vậy \(x\) \(\in\) {-7; 6}
d; \(x-\dfrac{2}{9}\) = \(\dfrac{1}{6}\)
\(x\) = \(\dfrac{1}{6}\) + \(\dfrac{2}{9}\)
\(x\) = \(\dfrac{7}{18}\)
Vậy \(x\) = \(\dfrac{7}{18}\)
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125.(-8).(-25).9.4.1002:3
=125.(-8).(-25).4.1002.9:3
=(-1000).(-100).10000.3
=3000000000
Chúc bn học tốt
![](https://rs.olm.vn/images/avt/0.png?1311)
nhân chéo chia ngang
x= -7*36/12=-21
muốn chắc chắn thì thử lại
\(\frac{-7}{12}=\frac{21}{36}\)theo quy đồng cũng đúng
Viết lại là:
\(\frac{-7}{12}=\frac{x}{36}\)
=> \(-7.36=12.x\)
=> \(-252=12.x\)
=> \(x=\frac{-252}{12}\)
=> \(x=-21\)
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minh giai y 1con y 2 neu can giup minh se giai cho
=(-1+3)+(-5+7)+....+(97-99)=-2+-2+...+-2(co 25 so 2)=-2.25=-50
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Ta có:
+) \(\frac{2013.2012-1}{2013.2012}=1-\frac{1}{2013.2012}\)
+) \(\frac{2012.2011-1}{2012.2011}=1-\frac{1}{2012.2011}\)
Vì \(\frac{1}{2013.2012}< \frac{1}{2012.2011}\Rightarrow1-\frac{1}{2013.2012}>1-\frac{1}{2012.2011}\)
Vậy \(\frac{2013.2012-1}{2013.2012}>\frac{2012.2011-1}{2012.2011}\)
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96 - 3(x+1 ) = 42
=> 3(x+1) = 96 - 42 = 54
=> x + 1 = 54 : 3 = 18
x + 1 = 18
=> x = 17
96 - 3 ( x + 1 ) = 42
3 ( x + 1 ) = 96 - 42
3 (x + 1 ) = 54
x + 1 = 54 : 3
x + 1 = 18
x = 18 - 1
x = 17
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7 ngay 6 dem khach san 5 sao tang 4 phing 3 2 nguoi 1 giuong o quan o ao
7 ngay 6 lan 5 gio 4 phut nga 3 ,2 thang 1 chai o say o ve
a) \(2x-\dfrac{2}{11}=1\dfrac{1}{5}\)
\(\Rightarrow2x=\dfrac{6}{5}+\dfrac{2}{11}\)
\(\Rightarrow2x=\dfrac{76}{55}\)
\(\Rightarrow x=\dfrac{76}{55}:2\)
\(\Rightarrow x=\dfrac{38}{55}\)
b) \(\dfrac{5}{9}+\dfrac{4}{3}x=\dfrac{-1}{3}\)
\(\Rightarrow\dfrac{4}{3}x=\dfrac{-1}{3}-\dfrac{5}{9}\)
\(\Rightarrow\dfrac{4}{3}x=-\dfrac{8}{9}\)
\(\Rightarrow x=-\dfrac{8}{9}:\dfrac{4}{3}\)
\(\Rightarrow x=-\dfrac{2}{3}\)
c) \(\dfrac{-3}{7}-\dfrac{3}{5}x=\dfrac{4}{5}+\dfrac{-2}{3}\)
\(\Rightarrow\dfrac{-3}{7}-\dfrac{3}{5}x=\dfrac{2}{15}\)
\(\Rightarrow\dfrac{3}{5}x=-\dfrac{3}{7}-\dfrac{2}{15}\)
\(\Rightarrow\dfrac{3}{5}x=\dfrac{-59}{105}\)
\(\Rightarrow x=\dfrac{-59}{105}:\dfrac{3}{5}\)
\(\Rightarrow x=-\dfrac{59}{63}\)
d) \(\dfrac{3x}{8}=\dfrac{-6}{15}\cdot\dfrac{5}{14}\)
\(\Rightarrow\dfrac{3x}{8}=\dfrac{-3}{7}\)
\(\Rightarrow8\cdot\dfrac{3x}{8}=8\cdot\dfrac{-3}{7}\)
\(\Rightarrow3x=-\dfrac{24}{7}\)
\(\Rightarrow x=\dfrac{-24}{7}:3\)
\(\Rightarrow x=-\dfrac{8}{7}\)