Question 129801
{{{N(x) -.4x^2 + 9x + 11}}}
This is a parabola that peaks at the 
midpoint of the 2 roots which are
found by applying the formula
{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}
I can decompose this into
{{{x[1] = (-b)/(2a) + sqrt( b^2-4*a*c )/(2a) }}}
and
{{{x[2] = (-b)/(2a) - sqrt( b^2-4*a*c )/(2a) }}}
The midpoint of these is {{{-(b/2a)}}}
The equation is in the form {{{y = ax^2 + bx + c}}}
{{{a = -.4}}}
{{{b = 9}}}
{{{-(b/2a) = -(9/(2*(-.4)))}}}
{{{-(b/2a) = 9/.8}}}
{{{-(b/2a) = 11.25}}}
This is days after concert starts when the ticket sales peak
when {{{N(x)}}}
{{{N(x) -.4x^2 + 9x + 11}}}
{{{N(11.25) = -.4*11.25^2 + 9*11.25 + 11}}}
{{{N(11.25) = -50.625 + 101.25 + 11}}}
{{{N(11.25) = 61.625}}}
This is the daily tickets sales peak
I'll plot the equation to check
{{{ graph( 600, 600, -5, 26, -5, 65, -.4x^2 + 9x + 11) }}}