If f(x)=x3−6x2+9xf(x) = x^3 - 6x^2 + 9xf(x)=x3−6x2+9x, on what interval is the function concave up?
(2,∞)(2, \infty)(2,∞)
(−∞,2)(-\infty, 2)(−∞,2)
(0,3)(0, 3)(0,3)
(−∞,∞)(-\infty, \infty)(−∞,∞)