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\(\dfrac{12}{7}:\dfrac{3}{14}=x:\dfrac{2}{5}\)
\(\Rightarrow8=x:\dfrac{2}{5}\)
\(\Rightarrow8.\dfrac{2}{5}=x\)
\(\Rightarrow\dfrac{16}{5}\)\(=x\)
Vậy \(x=\dfrac{16}{5}\)
\(\left[\left(3^{14}\times69+3^{14}\times12\right):3^{16}-7\right]:2^4\)
\(=\left[3^{14}\left(69+12\right):3^{16}-7\right]:2^4\)
\(=\left[3^{14}.81:3^{16}-7\right]:2^4\)
\(=\left[3^{14}.3^4:3^{16}-7\right]:2^4\)
\(=\left[3^2-7\right]:2^4\)
\(=2:2^4\)
\(=\dfrac{2}{16}=\dfrac{1}{8}\)
\(\left[\left(3^{14}.69+3^{14}.12\right):3^{16}-7\right]:2^4\\ =\left[3^{14}.\left(69+12\right):3^{16}-7\right]:2^4\\ =\left[3^{14}.81:3^{16}-7\right]:2^4\\ =\left[3^{14}.3^4:3^{16}-7\right]:2^4\\ =\left(3^2-7\right):2^4=2:2^4=\dfrac{1}{2^3}=\dfrac{1}{8}\)
a)
\(\begin{array}{l}x.\frac{{14}}{{27}} = \frac{{ - 7}}{9}\\x = \frac{{ - 7}}{9}:\frac{{14}}{{27}}\\x = \frac{{ - 7}}{9}.\frac{{27}}{{14}}\\x = \frac{{ - 3}}{2}\end{array}\)
Vậy \(x = \frac{{ - 3}}{2}\).
b)
\(\begin{array}{l}\left( {\frac{{ - 5}}{9}} \right):x = \frac{2}{3}\\x = \left( {\frac{{ - 5}}{9}} \right):\frac{2}{3}\\x = \left( {\frac{{ - 5}}{9}} \right).\frac{3}{2}\\x = \frac{{ - 5}}{6}\end{array}\)
Vậy \(x = \frac{{ - 5}}{6}\).
c)
\(\begin{array}{l}\frac{2}{5}:x = \frac{1}{{16}}:0,125\\\frac{2}{5}:x = \frac{1}{{16}}:\frac{1}{8}\\\frac{2}{5}:x = \frac{1}{{16}}.8\\\frac{2}{5}:x = \frac{1}{2}\\x = \frac{2}{5}:\frac{1}{2}\\x = \frac{2}{5}.2\\x = \frac{4}{5}\end{array}\)
Vậy \(x = \frac{4}{5}\)
d)
\(\begin{array}{l} - \frac{5}{{12}}x = \frac{2}{3} - \frac{1}{2}\\ - \frac{5}{{12}}x = \frac{4}{6} - \frac{3}{6}\\ - \frac{5}{{12}}x = \frac{1}{6}\\x = \frac{1}{6}:\left( { - \frac{5}{{12}}} \right)\\x = \frac{1}{6}.\frac{{ - 12}}{5}\\x = \frac{{ - 2}}{5}\end{array}\)
Vậy \(x = \frac{{ - 2}}{5}\).
Chú ý: Khi trình bày lời giải bài tìm x, sau khi tính xong, ta phải kết luận.
a, 2x-3-x+5=x+2-x+1
2x-x-x+x=2+1+3-5
0x=1
=> x thuộc rỗng (vì số nào nhân với 0 cũng bằng 0)
b, 2x-2-5x+10=-10
2x-5x=-10+2-10
-3x=2
x=-2/3
c, 2x-10-3x+21=14
2x-3x=14+10-21
-x=3
x=-3
d, 5x-6-2x+6=12
5x-2x=12+6-6
3x=12
x=4
e, -35+7x-2x+10=15
7x-2x=15+35-10
5x=40
x=8
\(\dfrac{12}{7}:\dfrac{3}{14}=x:\dfrac{2}{5}\)
\(\dfrac{12}{7}\times\dfrac{14}{3}=x:\dfrac{2}{5}\)
\(8=x:\dfrac{2}{5}\)
\(x=8\times\dfrac{2}{5}\)
\(x=\dfrac{16}{5}\)
8 = x : 2/5
x : 2/5 = 8
x = 8 x 2/5
x = 16/5
vậy x = 16/5