3x^2 +2x -16 =0 if a = 3 b=2 how can x =[-b +minus (b^2 - 4ac)] be /2a and I get 192 please reexplain

Question

I don't understand this answer as if a = 3 b= 2 and c = -16 wouldn't a be 3 and wouldn't 196 be 192/6? Can I have it redone or explained a little more?

Answer 1

ax² + bx + c = 0
x_1,2 = (-b ± √D) / 2a , D = b² - 4ac

3x² + 2x - 16 = 0
D = 2² – 4 · 3 · (-16) = 196
x_1,2 = (-2 ± √196) / 2 · 3 = (-2 ± 14)/6 = (-1 ± 7)/3
x₁ = (-1 - 7)/3 = -8/3 
x₂ = (-1 + 7)/3 = 6/3 = 2

1. 3 · (-8/3)² + 2(-8/3) -16 = 0  
    64/3 - 16/3 - 16 = 0
            0 = 0
2. 3 · 2² + 2 · 2 - 16 = 0
     12 + 4 - 16 = 0
           0 = 0

Answer 2

Note this will factor cleanly.

(3x + 8)(x - 2) = 0

x = -8/3,  2