Over which interval is the graph of f(x) = 1/2x^2 + 5x + 6 increasing?
(–6.5, ∞)
(–5, ∞)
(–∞, –5)
(–∞, –6.5)
(–6.5, ∞)
(–5, ∞)
(–∞, –5)
(–∞, –6.5)