Rhett is solving the quadratic equation zero equals x2 minus 2x -3 using the quadratic formula which shows the correct substitution of the value of a a, b and c into the quadratic formula

X^2-2x -3 =0
a =1 b =-2 and c = -3 

x = - (-2) +/- sqrt (-2)^2 - 4(1)(-3)
     
                   2(1)

 x = + 2 +/- sqrt [(4) - 4(-3)]
       
                    2

 x = +2 +/- sqrt [4 + 12]
       
                   2
x = +2 +/- sqrt[16]
     
              2

x = +2 +/- (4)
     
             2

x = 2 + 4    or 2 -4 
             
         2               2

x = 6/2      or   -2/2

x = 3   or x = -1