(2x - 3)*(x+4) =
2x*x + 2x*4 - 3*x - 3*4 =
2x^2 + 8x - 3x - 12 =
2x^2 + 5X - 12 =
a = 2; b = 5, c = - 12
Δ = b^2 - 4.a.c
Δ = 5^2 - 4.2.(-12)
Δ = 25 - 8. (-12)
Δ = 25 + 96
Δ = 121
x = -b±√Δ / 2.a
x = -5±√121 / 2.2
x = -5±11 / 4
x' = -5-11 / 4 = -16/4 => x' = -4
x" = -5+11 / 4 = 6/4 (÷2) => x" = 3/2
