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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
a: 1,2m=12dm
Diện tích xung quanh bể cá là:
\(\left(12+8\right)\cdot2\cdot6=12\cdot20=240\left(dm^2\right)\)
Diện tích kính dùng làm bể cá là:
\(240+12\cdot8=336\left(dm^2\right)\)
b: Thể tích bể cá là:
\(12\cdot8\cdot6=48\cdot12=576\left(dm^3\right)\)
c: Thể tích nước trong bể là:
\(576\cdot\dfrac{2}{3}=384\left(lít\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
16: \(0\cdot\dfrac{195}{2007}=0\)
1: \(\dfrac{4}{5}\cdot\dfrac{1}{2}=\dfrac{4\cdot1}{5\cdot2}=\dfrac{4}{10}=\dfrac{2}{5}\)
2: \(\dfrac{3}{7}\cdot\dfrac{3}{5}=\dfrac{3\cdot3}{5\cdot7}=\dfrac{9}{35}\)
3: \(\dfrac{1}{2}\cdot\dfrac{2}{9}=\dfrac{1\cdot2}{2\cdot9}=\dfrac{2}{18}=\dfrac{1}{9}\)
4: \(\dfrac{1}{5}\cdot\dfrac{3}{8}=\dfrac{1\cdot3}{5\cdot8}=\dfrac{3}{40}\)
5: \(7\cdot\dfrac{6}{7}=\dfrac{7\cdot6}{7}=\dfrac{42}{7}=6\)
6: \(5\cdot\dfrac{15}{4}=\dfrac{5\cdot15}{4}=\dfrac{75}{4}\)
7: \(\dfrac{4}{8}\cdot\dfrac{5}{3}=\dfrac{4\cdot5}{8\cdot3}=\dfrac{20}{24}=\dfrac{5}{6}\)
8: \(\dfrac{4}{9}\cdot\dfrac{2}{3}=\dfrac{4\cdot2}{9\cdot3}=\dfrac{8}{27}\)
9: \(\dfrac{5}{6}\cdot\dfrac{4}{7}=\dfrac{5\cdot4}{6\cdot7}=\dfrac{20}{42}=\dfrac{5}{21}\)
10: \(\dfrac{7}{9}\cdot\dfrac{3}{5}=\dfrac{7\cdot3}{5\cdot9}=\dfrac{21}{45}=\dfrac{7}{15}\)
11: \(9\cdot\dfrac{5}{6}=\dfrac{9\cdot5}{6}=\dfrac{45}{6}=\dfrac{15}{2}\)
12: \(\dfrac{2}{5}\cdot15=\dfrac{2\cdot15}{5}=\dfrac{30}{5}=6\)
13: \(\dfrac{5}{6}\cdot\dfrac{7}{8}=\dfrac{5\cdot7}{6\cdot8}=\dfrac{35}{48}\)
14: \(4\cdot\dfrac{3}{16}=\dfrac{4\cdot3}{16}=\dfrac{12}{16}=\dfrac{3}{4}\)
15: \(\dfrac{7}{3}\cdot\dfrac{3}{2}=\dfrac{7\cdot3}{3\cdot2}=\dfrac{21}{6}=\dfrac{7}{2}\)
17: \(\dfrac{15}{3}\cdot\dfrac{3}{5}=\dfrac{15\cdot3}{3\cdot5}=\dfrac{45}{15}=3\)
18: \(\dfrac{7}{5}\cdot\dfrac{15}{14}=\dfrac{7\cdot15}{5\cdot14}=\dfrac{105}{70}=\dfrac{3}{2}\)
19: \(20\cdot\dfrac{7}{4}=\dfrac{20\cdot7}{4}=\dfrac{140}{4}=35\)
20: \(\dfrac{11}{3}\cdot\dfrac{26}{7}=\dfrac{11\cdot26}{3\cdot7}=\dfrac{286}{21}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
`630 : x - 24 = 18`
`630 : x = 18 + 24`
`630 : x = 42`
`x = 630 : 42`
`x = 15`
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có:
`4x-5y-6xy+7=0`
`⇒(4x-6xy)-5y+7=0`
`⇒2x(2-3y)-5y+7=0`
`⇒6x(2-3y)-15y+21=0`
`⇒6x(2-3y)+21-15y=0`
`⇒6x(2-3y)+(10-15y)+11=0`
`⇒-6x(3y-2)-(15y-10)+11=0`
`⇒-6x(3y-2)-5(3y-2)=-11`
`⇒(3y-2)(6x+5)=11`
Mà `x,y∈Z`
Ta có bảng:
3y - 2 | 1 | -1 | -11 | 11 |
6x + 5 | 11 | -11 | -1 | 1 |
y | 1 | `1/3` (loại) | -3 | `13/3` (loại) |
x | 1 | `-16/6`(loại) | -1 | `-2/3` (loại) |
Vậy: ...