(1,5 điểm) Tìm x , biết: a) 9 ⋅ ( x + 2 ) − 28 = 26. b) ( − 6 + 3 x ) : 5 = − 18. c) ( 4 − x ) 3 + 17 = − 10.

a) \(9 \cdot \left( {x + 2} \right) - 28 = 26\)

\(9 \cdot \left( {x + 2} \right) = 54\)

\(x + 2 = 6\)

\(x = 4\)

Vậy \(x = 4.\)

b) \(\left( { - 6 + 3x} \right):5 = - 18\)

\( - 6 + 3x = - 90\)

\(3x = - 84\)

\(x = - 28\).

Vậy \(x = - 28\).

c) \({\left( {4 - x} \right)^3} + 17 = - 10\)

\({\left( {4 - x} \right)^3} = - 27\)

\({\left( {4 - x} \right)^3} = {\left( { - 3} \right)^3}\)

Suy ra \(4 - x = - 3\)

\(x = 4 - \left( { - 3} \right)\)

\(x = 7\)

Vậy \(x = 7.\)