a) 3x (12x - 4) - 9x (4x - 3) = 30

     36x\(^2\) – 12x – 36x\(^2\) + 27x = 30

                                     15x = 30

                                     Vậy x = 2.

b) x (5 - 2x) + 2x (x - 1) = 15

       5x – 2x\(^2\) + 2x\(^2\) – 2x = 15

                                 3x = 15

                                   x =5

a) 3x (12x - 4) - 9x (4x - 3) = 30

\(\Leftrightarrow\)36x²  – 12x – 36x²  + 27x = 30

\(\Leftrightarrow\)15x = 30

\(\Leftrightarrow\)x = 2

b) x (5 - 2x) + 2x (x - 1) = 15

\(\Leftrightarrow\)5x – 2x^​2  + 2x²  – 2x = 15

\(\Leftrightarrow\)3x = 15

\(\Leftrightarrow\)x =5