Reinterpreting: "cost per unit" is standard, and we must minimize \( P(x) = C(x)/x \). But if \( C(x) = 5000 + 120x - 0.5x^2 \), then for large \( x \), the \( -0.5x^2 \) dominates and cost per unit becomes negative — impossible. - go-checkin.com