Tìm (x), biết:

a) \(12 - x = 37\)

\(x = 12 - 37\)

\(x =  - 25\)

Vậy \(x =  - 25\).

b) \(\left( {x - 15} \right):4 = {5^2} - {2^3}\)

\(\left( {x - 15} \right):4 = 25 - 8\)

\(\left( {x - 15} \right):4 = 17\)

\(x - 15 = 68\)

\(x = 83\)

Vậy \(x = 83\).

c) \( - 7\left( {x + 9} \right) + \left( { - 21} \right) = 35\)

\( - 7\left( {x + 9} \right) = 35 + 21\)

\( - 7\left( {x + 9} \right) = 56\)

\(x + 9 = 56:\left( { - 7} \right)\)

\(x + 9 =  - 8\)

\(x =  - 8 - 9\)

\(x =  - 17\)

Vậy \(x =  - 17\).

d) \(2{\left( {x - 6} \right)^2} - 1 = 49\)

\(2{\left( {x - 6} \right)^2} = 50\)

  \({\left( {x - 6} \right)^2} = 25\)

Trường hợp 1:

\(x - 6 = 5\)

\(x = 11\)

Vậy \(x \in \left\{ {11;1} \right\}\).

Trường hợp 2:

\(x - 6 =  - 5\)

\(x = 1\)