Tìm \(x\):a)\(165 - \left( {35:x + 3} \right).19 =...

B

- Hướng dẫn giải

Phương pháp giải:

+ Ta thực hiện tính trong ngoặc tròn trước rồi đến ngoặc vuông.

+ Ta thực hiện phép tính nâng lũy thừa trước rồi đến nhân chia, cuối cùng đến cộng trừ.

Giải chi tiết:

\(\begin{array}{l}{\rm{a)}}165 - \left( {35:x + 3} \right).19 = 13\\\left( {35:x + 3} \right).19\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 165 - 13\\\left( {35:x + 3} \right).19\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 152\\35:x + 3\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 152:19\\35:x + 3\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 8\\35:x\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 8 - 3\\35:x\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 5\\x\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 35:5\\x\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 7.\end{array}\)   

Vậy \(x = 7\)                           

 \(\begin{array}{l}{\rm{b)}}697:\left[ {\left( {15.x + 364} \right):x} \right] = 17\\\left( {15x + 364} \right):x = 697:17\\\left( {15x + 364} \right):x = 41\\15:x + 364:x = 41\\364:x = 41 - 15\\364:x = 26\\x = 364:26\\x = 14\end{array}\)

Vậy  \(x = 14\)

\(\begin{array}{l}{\rm{c)}}{5^{x - 2}} - {3^2} = {2^4} - \left( {{2^{8 + 4}} - {2^{10 + 2}}} \right)\\{5^{x - 2}} - {3^2}\,\,\,\,\,\,\, = {2^4} - \left( {{2^{12}} - {2^{12}}} \right)\\{5^{x - 2}} - {3^2}\,\,\,\,\,\,\, = {2^4} - 0 = {2^4}\\{5^{x - 2}} - 9\,\,\,\,\,\,\,\,\, = 16\\{5^{x - 2}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 16 + 9\\{5^{x - 2}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 25 = {5^2}\\x - 2\,\,\,\,\,\,\,\,\,\,\,\,\, = 2\\x\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 2 + 2\\x\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 4.\end{array}\)

Vậy \(x = 4\)

Chọn B.