I was giving an example that completely lost me.

The quadratic function is: 2x^2 - 5x - 12

Let y = 0, factor, and solve.

0= (2x + 3)(x - 4)

x = -3/2 or x = 4

The mid value is:

x = -3/2 + 4

________

2

= -3/2 + 8/2

_________

2

= 5/2/2

= 5/2 x 1/2

= 5/4

Im completely confused at the step where the 4 became 8/2, and the steps beyond, any help?