Toán Lớp 7: Cứu em với mọi người
Câu a -7/15+-5/19
Câu b -9/20_-3/20:3/4
Câu c -8/97.4/5+7/8.-8/97+–3/4.8/97
Câu d (-2/3_3/4):7/279+(2/3+3/4):7/279
Bài 2
a. -2/3-X=-1/5
b. 3/4 +1/4:X=2/5
c. 4/5-(0,3+X)_-2/5
d.4/5X-3√4/5=-3/5
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a)\dfrac{{ – 7}}{{15}} + \dfrac{{ – 5}}{{19}}\\
= \dfrac{{ – 7.19 – 5.15}}{{15.19}}\\
= \dfrac{{ – 208}}{{285}}\\
b)\dfrac{{ – 9}}{{20}} – \dfrac{3}{{20}}:\dfrac{3}{4}\\
= \dfrac{{ – 9}}{{20}} – \dfrac{3}{{20}}.\dfrac{4}{3}\\
= \dfrac{{ – 9}}{{20}} – \dfrac{4}{{20}}\\
= \dfrac{{ – 13}}{{20}}\\
c)\dfrac{{ – 8}}{{97}}.\dfrac{4}{5} + \dfrac{7}{8}.\dfrac{{ – 8}}{{97}} + \dfrac{{ – 3}}{4}.\dfrac{8}{{97}}\\
= \dfrac{8}{{97}}\left( {\dfrac{{ – 4}}{5} – \dfrac{7}{8} – \dfrac{3}{4}} \right)\\
= \dfrac{8}{{97}}.\dfrac{{ – 97}}{{40}}\\
= \dfrac{{ – 1}}{5}\\
d)\left( { – \dfrac{2}{3} – \dfrac{3}{4}} \right):\dfrac{7}{{279}} + \left( {\dfrac{2}{3} + \dfrac{3}{4}} \right):\dfrac{7}{{279}}\\
= – \left( {\dfrac{2}{3} + \dfrac{3}{4}} \right):\dfrac{7}{{279}} + \left( {\dfrac{2}{3} + \dfrac{3}{4}} \right):\dfrac{7}{{279}}\\
= 0\\
B2)a)\dfrac{{ – 2}}{3} – x = \dfrac{{ – 1}}{5}\\
\Leftrightarrow x = \dfrac{{ – 2}}{3} + \dfrac{1}{5}\\
\Leftrightarrow x = – \dfrac{7}{{15}}\\
Vậy\,x = – \dfrac{7}{{15}}\\
b)\dfrac{3}{4} + \dfrac{1}{4}x = \dfrac{2}{5}\\
\Leftrightarrow \dfrac{1}{4}x = \dfrac{2}{5} – \dfrac{3}{4}\\
\Leftrightarrow \dfrac{1}{4}x = \dfrac{{ – 7}}{{20}}\\
\Leftrightarrow x = – \dfrac{7}{{20}}.4\\
\Leftrightarrow x = – \dfrac{7}{5}\\
Vậy\,x = – \dfrac{7}{5}\\
c)\dfrac{4}{5} – \left( {0,3 + x} \right) = – \dfrac{2}{5}\\
\Leftrightarrow 0,3 + x = \dfrac{4}{5} + \dfrac{2}{5}\\
\Leftrightarrow \dfrac{3}{{10}} + x = \dfrac{6}{5}\\
\Leftrightarrow x = \dfrac{6}{5} – \dfrac{3}{{10}}\\
\Leftrightarrow x = \dfrac{9}{{10}}\\
Vậy\,x = \dfrac{9}{{10}}\\
d)\dfrac{4}{5}x – \dfrac{{3\sqrt 4 }}{5} = – \dfrac{3}{5}\\
\Leftrightarrow 4x – 3.2 = – 3\\
\Leftrightarrow 4x = – 3 + 6\\
\Leftrightarrow 4x = 3\\
\Leftrightarrow x = \dfrac{3}{4}\\
Vậy\,x = \dfrac{3}{4}
\end{array}$