X-14=9
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a: \(=\dfrac{5}{14}\left(\dfrac{2}{9}+\dfrac{7}{9}+1\right)=\dfrac{5}{14}\cdot2=\dfrac{5}{7}\)
b: \(=\dfrac{6}{8}\left(\dfrac{6}{7}-6\right)=\dfrac{6}{8}\cdot\dfrac{-36}{7}=\dfrac{-216}{56}=\dfrac{-27}{7}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Đề Bài :\(\frac{9}{14}\)- \(\frac{x}{7}\): \(\frac{5}{3}\)= \(\frac{3}{14}\)
ta có : \(\frac{9}{14}\)- \(\frac{x}{7}\)= \(\frac{3}{14}\)x \(\frac{5}{3}\)= \(\frac{5}{14}\)
\(\frac{x}{7}\)= \(\frac{9}{14}\)- \(\frac{5}{14}\)= \(\frac{4}{14}\)
\(\frac{4}{14}\)= \(\frac{x}{7}\)=> \(\frac{4}{14}\)= \(\frac{2}{7}\)=> x = 2
![](https://rs.olm.vn/images/avt/0.png?1311)
X × 14/9 - X × 5/9 = 13
X × (14/9 - 5/9) = 13
X × 1 = 13
X = 13
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\(\dfrac{9}{14}\times13+\dfrac{9}{14}\)
\(=\dfrac{9}{14}\times13+\dfrac{9}{14}\times1\)
\(=\dfrac{9}{14}\times\left(13+1\right)\)
\(=\dfrac{9}{14}\times14\)
\(=\dfrac{126}{14}\) \(=9\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{14}{9}\) x \(\dfrac{11}{8}-\dfrac{3}{8}\) x \(\dfrac{14}{9}\)
\(=\dfrac{14}{9}\) x \(\left(\dfrac{11}{8}-\dfrac{3}{8}\right)\)
\(=\dfrac{14}{9}\) x \(\dfrac{8}{8}=\dfrac{14}{9}\) x \(1\)
\(=\dfrac{14}{9}\)
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\(\frac{9}{14}-\frac{x}{7}:\frac{5}{3}=\frac{3}{14}\Leftrightarrow\frac{9}{14}-\frac{3x}{35}=\frac{3}{14}\Leftrightarrow\frac{3x}{35}=\frac{3}{7}\Leftrightarrow3x=15\Leftrightarrow x=5\)
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`-3/5xx9/14-3/5xx5/14+3/5`
`=(-3/5+3/5)xx(9/14+5/14)xx3/5`
`=0xx14xx3/5`
`=0xx1xx3/5`
`=0xx3/5`
`=0`
`@Nae`
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\(\frac{1}{4\cdot9}+\frac{1}{9\cdot14}+\frac{1}{14\cdot19}+...+\frac{1}{1999+2004}\).
Có sai đề không vậy???
Sửa đề một chút :v
\(\frac{1}{4\cdot9}+\frac{1}{9\cdot14}+\frac{1}{14\cdot19}+...+\frac{1}{1999\cdot2004}\)
\(=\frac{1}{5}\left[\frac{5}{4\cdot9}+\frac{5}{9\cdot14}+\frac{5}{14\cdot19}+...+\frac{5}{1999\cdot2004}\right]\)
\(=\frac{1}{5}\left[\frac{1}{4}-\frac{1}{9}+\frac{1}{9}-\frac{1}{14}+...+\frac{1}{1999}-\frac{1}{2004}\right]\)
\(=\frac{1}{5}\left[\frac{1}{4}-\frac{1}{2004}\right]\)
\(=\frac{1}{5}\cdot\frac{125}{501}=\frac{25}{501}\)
Đặt A =1/4 x 9 + 1/9 x 14 + 1/14 x 19 +...+ 1/1999 + 2004. Ta có:
A= 1/4 x 9 + 1/9 x 14 + 1/14 x 19 +...+ 1/1999 + 2004
5A= 5/4 x 9 + 5/9 x 14 + 5/14 x 19 +...+ 5/1999 + 2004
5A= 1/4 - 1/9 + 1/9 - 1/14 + 1/14 - 1/19 +...+ 1/1999 - 1/2004
5A= 1/4 - 1/2004
A= (1/4 - 1/2004)/5
x = 14 + 9
x = 23
k cho mk nhe mai mot mk k lại cho
\(x-14=9\)
\(x=9+14\)
\(x=23\)
ngo thi kim thu
Toán lớp 2 chúc bn học giỏi!