Question 536477
{{{ x = 1 }}}, {{{ N(1) }}} 1st day and sales for 1st day
{{{ x = 2 }}}, {{{ N(2) }}} 2nd day and sales for 2nd day
{{{ x = 3 }}}, {{{ N(3) }}} 3rd day and sales for 3rd day
etc . . .
{{{ N(x)=-.4x^2 + 8x + 14 }}}
The minus in front of the x-squared term tells me 
that {{{ N(x) }}} has a max and not a min.
The max, or vertex, of a parabola is at {{{ x[max] = -b/(2a) }}}
{{{ a = -.4 }}}
{{{ b = 8 }}}
{{{ x[max] = -8/(2*(-.4)) }}}
{{{ x[max] = -8/-.8 }}}
{{{ x[max] = 10 }}}
Now find {{{ N(10) }}}
{{{ N(10) = -.4*10^2 + 8*10 + 14 }}}
{{{ N(10) = -40 + 80 + 14 }}}
{{{ N(10) = 54 }}}
The max daily ticket sales occur 10 days after concert
is announced and the sales on the 10th day are $54
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To check to see if this is the max, find {{{ N(9.9) }}}
and {{{ N(10.1) }}}. They should both be slightly less
than {{{ 54 }}}