The question is from http://www.xtremepapers.com/CIE/International A And AS Level/9709 - Mathematics/9709_w10_qp_13.pdf question no. 7 (i). I think it should be more than easy for a functions fanatic( or someone who does math regularly for that matter) to get the right answer, but as one can clearly see I can't. The answer says 0 < f(x) < 4. But I am getting 0 ≤ f(x) ≤ 4. Why are 0 and 4 not inclusive? Because it clearly says in the question X CAN take up 0 and 6, for which the corresponding Y value should be 0 and 4 respectively.