Đáp án đúng: B
Giải chi tiết:\(\begin{array}{l}{\rm{a)}}{\rm{ }}{\left( {7x - 11} \right)^3} = {2^5}{.5^2} + 200\\{\left( {7x - 11} \right)^3}\,\,\,\,\,\,\,\, = 32.25 + 200\\{\left( {7x - 11} \right)^3}\,\,\,\,\,\,\,\, = 800 + 200\\{\left( {7x - 11} \right)^3}\,\,\,\,\,\,\,\, = 1000\\{\left( {7x - 11} \right)^3}\,\,\,\,\,\,\,\, = {10^3}\\7x - 11\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 10\\7x\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 10 + 11\\7x\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 21\\x\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 21:7\\x\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 3\end{array}\)
\(\begin{array}{l}{\rm{b)}}{\rm{ }}{5^{x - 2}} - {3^2} = {2^4} - \left( {{6^8}:{6^6} - {6^2}} \right)\\{5^{x - 2}} - 9\,\,\,\,\,\,\,\,\,\,\, = 16 - \left( {{6^{8 - 6}} - {6^2}} \right)\\{5^{x - 2}} - 9\,\,\,\,\,\,\,\,\,\,\, = 16 - \left( {{6^2} - {6^2}} \right)\\{5^{x - 2}} - 9\,\,\,\,\,\,\,\,\,\,\, = 16 - 0\\{5^{x - 2}} - 9\,\,\,\,\,\,\,\,\,\,\, = 16\\{5^{x - 2}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 16 + 9\\{5^{x - 2}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 25\\{5^{x - 2}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = {5^2}\\x - 2\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 2\\x\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 2 + 2\\x\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 4.\end{array}\)
Chọn B.
