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\(\frac{7}{x}=\frac{y}{27}=-\frac{42}{54}\)
\(\Leftrightarrow\frac{7}{x}=\frac{y}{27}=-\frac{7}{9}\)
Có \(\frac{7}{x}=-\frac{7}{9}\)
\(\Leftrightarrow x=-9\)
Lại có \(\frac{y}{27}=-\frac{7}{9}\)
\(\Leftrightarrow x=-21\)
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\(\dfrac{1}{1.4}+\dfrac{1}{4.2}+\dfrac{1}{2.8}+\dfrac{1}{8.4}+\dfrac{1}{4.16}+\dfrac{1}{16.8}\)
= \(\dfrac{1}{4}.\left(1+\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{16}+\dfrac{1}{32}\right)\)
= \(\dfrac{1}{4}.\left(\dfrac{3}{2}+\dfrac{3}{8}+\dfrac{3}{32}\right)\)
= \(\dfrac{1}{4}.\dfrac{3}{2}\left(1+\dfrac{1}{4}+\dfrac{1}{16}\right)\)
= \(\dfrac{1}{4}.\dfrac{3}{2}\left(\dfrac{16}{16}+\dfrac{4}{16}+\dfrac{1}{16}\right)\)
= \(\dfrac{3}{8}.\dfrac{21}{16}\)
= \(\dfrac{63}{128}\)
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- Tất cả các đoạn thẳng có trong hình vẽ là : MP ; MQ ; MN ; NQ ; PQ ; NP
\(\Rightarrow\) Chọn \(B\)
_HT_
\(324\cdot36-254\cdot72+18\cdot368\)
\(=18\cdot\left(324\cdot2-254\cdot3+368\right)\)
\(=18\cdot\left(648-1016+368\right)\)
\(=18\cdot\left(1016-1016\right)\)
\(=18\cdot0\)
\(=0\)
\(7364-\left(8475-4555\right)-364+445+475\)
\(=7364-8475+4555-364+445+475\)
\(=\left(7364-364\right)-\left(8475-475\right)+\left(4555+445\right)\)
\(=7000-8000+5000\)
\(=4000\)
\(21\cdot32\cdot43-21\cdot32\cdot40-21\cdot32\cdot3\)
\(=21\cdot32\cdot\left(43-40-3\right)\)
\(=21\cdot32\cdot0\)
\(=21\cdot0\)
\(=0\)