Đáp án:
$\begin{array}{l}
1)c)38x - x.12 - x.16 = 40\\
\Leftrightarrow x.\left( {38 - 12 - 16} \right) = 40\\
\Leftrightarrow x.10 = 40\\
\Leftrightarrow x = 4\\
Vậy\,x = 4\\
d)280 - x.9 - x = 80\\
\Leftrightarrow 10x = 200\\
\Leftrightarrow x = 20\\
Vậy\,x = 20\\
B2)\\
c){\left( {x + 2} \right)^3} = {\left( {2x} \right)^3}\\
\Leftrightarrow x + 2 = 2x\\
\Leftrightarrow x = 2\\
Vậy\,x = 2\\
d){\left( {2x - 1} \right)^7} = {x^7}\\
\Leftrightarrow 2x - 1 = x\\
\Leftrightarrow x = 1\\
Vậy\,x = 1\\
B3)\\
a){3^{20}}\\
{27^4} = {\left( {{3^3}} \right)^4} = {3^{12}} < {3^{20}}\\
Vậy\,{3^{20}} > {27^4}\\
b){5^{34}}\\
{25.5^{30}} = {5^2}{.5^{30}} = {5^{32}} < {5^{34}}\\
Vậy\,{5^{34}} > {25.5^{30}}\\
c){2^{25}}\\
{16^6} = {\left( {{2^4}} \right)^6} = {2^{24}} < {2^{25}}\\
Vậy\,{2^{25}} > {16^6}
\end{array}$
d) Thiếu đề
