1. The problem statement, all variables and given/known data A soccer ball is kicked into the air from a platform. The height of the ball, in metres, t seconds after it is kicked is modelled by h(t) = -4.9t^2 + 13.5t + 1.2. I solved for the expression that represents the average rate of change of height over the interval 2<= t <= (2+h) and got which is correct (according to the answer key): [-4.9(2+h)^2 + 13.5(2+h) - 7.4] / h For what values of h is the expression above not valid? The answer in the back states h>0.84; at 2.84 s, h = 0. I understood how they got h>0.84 by finding the zeroes of the quadratic equation to get 2.84 and then subbing that into the inequality to get the change (h) to be 0.84. Therefore since t !> 2.84 h !> 0.84. But how do they get at 2.84 s, h != 0 as restrictions? How did they get 0.84 and 2.84 in the restrictions. This question is a bit confusing to me. Can anyone help me find the answer?