New member tormented by bijective functions

Hello everyone, i'm Barbie.

I'm glad to meet u all, never been in a forum before so forgive me if i break the rules.

I'm studying discrete maths...i understand functions upto a point. But i'm lost at the formula below:

a[(x + b/2a)^{2})- (b^{2} - 4ac)/4a^{2}]

My Maths teacher used it to solve the bijective function below:

f(x) = 4x^{2} - 2x + 3, write f(x) in the form f(x) = a(x-b)^{2 }+ c, (where x > p if f is invertible)

I would like to know what the formula is and how its used.

Thankyou.