Hi, I'm in need of some help putting together this proof. I'm not sure if it's just harder than it looks, or I need to spend more time learning how to put them together. 1. The problem statement, all variables and given/known data Show that [itex]f(x) = 9x^2 + 3x[/itex] is strictly increasing on the interval [itex](0, 10][/itex] 2. Relevant equations 3. The attempt at a solution I realise there are various arguments involving the turning point of a quadratic equation, but I don't think this is the type of answer that they're looking for. Let [itex]u < v[/itex] be two elements of the interval [itex](0, 10][/itex]. Then from [itex]f(u) < f(v)[/itex] we obtain: [tex]9u^2 + 3u < 9v^2 + 3v[/tex], [tex]9u^2 + 3u - 9v^2 + 3v < 0[/tex] From here, I think I need to get to [itex]u < v[/itex], but I can't see how to do it. Thanks for any help.