Tìm x, biết: a) 5x − 2^3 = 3^3

a) \(5x - {2^3} = {3^3}\)

\(5x - 8 = 27\)

\(5x = 27 + 8\)

\(5x = 35\)

\(x = 35:5\)

\(x = 7\)

Vậy \(x = 7\).

b) \(51 - 3\left( {x + 2} \right) = 60\)

\(3\left( {x + 2} \right) = 51 - 60\)

\(3\left( {x + 2} \right) = - 9\)

\(x + 2 =  - 9:3\)

   \(x + 2 = - 3\)

   \(x = - 3 - 2\)

   \(x = - 5\).

Vậy \(x = - 5\).

c) \(\left[ {{{\left( {x + 3} \right)}^2} - 8} \right] \cdot 2 = - 14\)

      \({\left( {x + 3} \right)^2} - 8 = - 14:2\)

\({\left( {x + 3} \right)^2} - 8 = - 7\)

\({\left( {x + 3} \right)^2} =  - 7 + 8\)

\({\left( {x + 3} \right)^2} = 1\)

Trường hợp 1:

\(x + 3 = 1\)

\(x = - 2\)

Vậy \(x \in \left\{ { - 2; - 4} \right\}\).

Trường hợp 2:

\(x + 3 = - 1\)

\(x = - 4\)