Explanation:
first make the coefficient of b square unity by dividing all the numbers by 2. then,
b^2-5b +6=0
second shift the constant term to R.H.S
b^2-5b=-6
then add (1/2 of coefficient b)^2 on both sides
b^2-5b+(5/2)^2=-6+(5/2)^2
b^2-5b+25/4=-6+25/4
then express the L.H.S as a perfect square of suitable binomial expression and simplify R.H.S.
(b-5/4)^2=13/2
then take square roots both sides
b=5/4+_square root of 13/2
s.s={5/4+_square root of 13/2}