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(x-3)(x+4) =0

x-3 = 0                       x+4 =0

x = 3                          x = -4

x(2x+6) =0

x = 0                     2x+6 =0

                               2x = -6

                               x = -6/2 = -3

(2x+5)(x-7 )=0

2x+5 = 0             x-7 =0

2x = -5                 x = 7

x = -5/2

(4x+7)(3-7x) =0

4x+7 =0                3-7x =0

4x = -7                      -7x = -3

x = -7/4                       x = -3/-7 = 3/7