Tìm x, biết x2 -9 =0

1/ x2 – 9 = 0                                                       2/ 3x3 – 12x = 0                        

3/  x(2x – 7) – (4x – 14) = 0                             4/ 7x2 – 28 = 0                    

5/  5x(x – 3) – 2x + 6  = 0                               6/ (12x - 5)(4x - 1) + (3x - 7)(1 - 16x) = 81

cần gấp ạ giúp đi tớ tặng quà choo