Question 408782
{{{ graph( 300, 200, -10, 50, -10, 90, -0.5x^2+11x+15) }}}
Now if we could just find the 2 x values where the graph
crosses the X axis. We can use the quadratic equation and get


*[invoke quadratic "x", -0.5, 11, 15 ]

so we get x=-1.2 and x=23.28. Now lets see 23.28 - (23.28+1.2)/2 = 11.
So it's 11 days of ticket sale increase from the -1.2 intercept. We probabily
want to start a day = 0 so take 1 day off and get 10 days to peak.