Question 561145
The minus sign means that the curve has a maximum
and not a minimum. 
As for the value, suppose I have {{{ y = -2x^2 + 4x + 1 }}}
The plot is:
{{{ graph( 400, 400, -5, 5, -5, 5, -2x^2 + 4x + 1  ) }}}
Now If I change it to {{{ y = -6x^2 + 4x + 1 }}}, the plot is
{{{ graph( 400, 400, -5, 5, -5, 5, -6x^2 + 4x + 1  ) }}}
This means a larger negative number would give you a
lower maximum profit and a smaller number of items
sold that will result in zero profit ( the x-intercept )