First, we get ax^2+bx+c. Next, we know that the line of symmetry is -b/2a. Since we know that there is a maximum value, the parabola is facing downwards, so a is negative. For random numbers, we can say that a = -0.5 and b=-10 (b needs to be negative for -b/2a to equal -10), getting -0.5x^2-10x+c. Plugging -10 in for x (since -10 is the middle it is the max), we get -50+100=50. Since the maximum needs to be 5, not 50, we subtract 45 from the answer to get it and therefore make c = -45, getting -0.5x^2-10x-45