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tính
1)\(\left(\dfrac{1}{2}\right)^2\)
\(=\dfrac{1}{2}\times\dfrac{1}{2}\)
\(=\dfrac{1}{4}\)
2)\(3,6^2\div1,2^2\)
\(=\left(\dfrac{18}{5}\right)^2\div\left(\dfrac{6}{5}\right)^2\)
\(=\left(\dfrac{18}{5}\times\dfrac{18}{5}\right)\div\left(\dfrac{6}{5}\times\dfrac{6}{5}\right)\)
\(=\dfrac{324}{25}\div\dfrac{36}{25}\)
\(=\dfrac{324}{25}\times\dfrac{25}{36}\)
\(=\dfrac{8100}{900}\)
\(=9\)
2: \(=\dfrac{203}{60}\cdot\dfrac{81}{1225}=\dfrac{783}{3500}\)
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Bài 1 : Ta thấy
\(\dfrac{10}{15}=\dfrac{2}{3};\dfrac{14}{21}=\dfrac{2}{3}\Rightarrow10:15=14:21\Rightarrow\dfrac{10}{15}=\dfrac{14}{21}\)
\(\dfrac{16}{\left(-4\right)}=-4;\dfrac{12}{\left(-3\right)}=-4\Rightarrow16:\left(-4\right)=12:\left(-3\right)\Rightarrow\dfrac{16}{\left(-4\right)}=\dfrac{12}{\left(-3\right)}=-4\)
\(\dfrac{\left(-5\right)}{15}=\dfrac{\left(-1,2\right)}{3,6}=-\dfrac{1}{3}\Rightarrow\left(-5\right):15=\left(-1,2\right):3,6\)
\(\dfrac{2}{3}:\dfrac{1}{4}=\dfrac{2}{3}.4=\dfrac{8}{3};\dfrac{16}{9}:\dfrac{16}{24}=\dfrac{16}{9}.\dfrac{24}{16}=\dfrac{8}{3}\)
\(\Rightarrow\left(\dfrac{2}{3}:\dfrac{1}{4}\right)=\left(\dfrac{16}{9}:\dfrac{16}{24}\right)=\dfrac{8}{3}\)
Bài 2 :
a) \(14.15=10.21\Rightarrow\dfrac{14}{10}=\dfrac{21}{15}=\dfrac{7}{5}\)
b) \(0,2.4,5=0,6.1,5\Rightarrow\dfrac{0,2}{0,6}=\dfrac{1,5}{4,5}=\dfrac{1}{3}\)
`30+2,8:(4/25 - 9/15 -1/6)`
`=30+2,8 :( -11/25-1/6)`
`=30+14/5 :(-19/150)`
`=30-60/13`
`=330/13`
0,75.1/2.25/6.(-1)^2=25/16.1=25/16
5,7+3,6-3.(1.2-2.8)=9,3-3.(-1,6)=9,3-(-4,8)=14,1