Hello,
D(x) = x(x + 1) -- 9(x -- 3) = x² + x -- 9x + 27 = x² -- 8x + 27.
D(x) = 2 ⇔ x² -- 8x + 27 = 2, or x² -- 8x + 25 = 0.
Δ = b² -- 4ac = (--8)² -- 4·1·25 = 64 -- 100 = --36, so Δ = --36.
√Δ = √(--36) = √(i²·6²) = 6i, so √Δ = 6i.
First solution is:
x₁ = (--b -- √Δ)/(2a) = (--(--8) -- 6i)/2 = 4 -- 3i, x₁ = 4 -- 3i.
x₂ = (--b + √Δ)/(2a) = (--(--8) + 6i)/2 = 4 + 3i, x₂ = 4 + 3i.
Did you understand the solution ?
Green eyes.
