Toán Lớp 7: A) – x + 1/7 = 3 – 11/2
B) 4^x = 4^3 . 4^5
C) 2/3 + 5/3 . x = 5/7
D) x/2 = y/3 và x + y = 10
E) x/4 = 2y/7 và x – 2y = 9
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Toán Lớp 7: A) – x + 1/7 = 3 – 11/2
B) 4^x = 4^3 . 4^5
C) 2/3 + 5/3 . x = 5/7
D) x/2 = y/3 và x + y = 10
E) x/4 = 2y/7 và x – 2y = 9
Giải gấp giúp em
Comments ( 1 )
a) – x + \dfrac{1}{7} = 3 – \dfrac{{11}}{2}\\
\Leftrightarrow x = \dfrac{1}{7} – 3 + \dfrac{{11}}{2}\\
\Leftrightarrow x = \dfrac{{2 – 3.14 + 11.7}}{{14}}\\
\Leftrightarrow x = \dfrac{{37}}{{14}}\\
Vậy\,x = \dfrac{{37}}{{14}}\\
b){4^x} = {4^3}{.4^5}\\
\Leftrightarrow {4^x} = {4^{3 + 5}}\\
\Leftrightarrow {4^x} = {4^8}\\
\Leftrightarrow x = 8\\
Vậy\,x = 8\\
c)\dfrac{2}{3} + \dfrac{5}{3}.x = \dfrac{5}{7}\\
\Leftrightarrow \dfrac{5}{3}.x = \dfrac{5}{7} – \dfrac{2}{3}\\
\Leftrightarrow \dfrac{5}{3}.x = \dfrac{1}{{21}}\\
\Leftrightarrow x = \dfrac{1}{{21}}.\dfrac{3}{5}\\
\Leftrightarrow x = \dfrac{1}{{35}}\\
Vậy\,x = \dfrac{1}{{35}}\\
d)\dfrac{x}{2} = \dfrac{y}{3} = \dfrac{{x + y}}{{2 + 3}} = \dfrac{{10}}{5} = 2\\
\Leftrightarrow \left\{ \begin{array}{l}
x = 2.2 = 4\\
y = 2.3 = 6
\end{array} \right.\\
Vậy\,x = 4;y = 6\\
e)\dfrac{x}{4} = \dfrac{{2y}}{7} = \dfrac{{x – 2y}}{{4 – 7}} = \dfrac{9}{{ – 3}} = – 3\\
\Leftrightarrow \left\{ \begin{array}{l}
x = – 3.4 = – 12\\
2y = – 3.7 = – 21
\end{array} \right.\\
\Leftrightarrow \left\{ \begin{array}{l}
x = – 12\\
y = – \dfrac{{21}}{2}
\end{array} \right.\\
Vậy\,x = – 12;y = – \dfrac{{21}}{2}
\end{array}$