Formula in Trendline
 

If I make a trendline from a graph Sales $ vs Time months.
y = -4E-10x^6 + 8E-05x^5 - 8.3566x^4 + 442188x^3 - 1E+10x^2 + 2E+14x - 1E+18

After making that ecuation on excel, I should just replace the month to get
approx sales volume, but it does not work. The month I enter should be a
series? like If I have 6 months on the graph then the next month should be
x=7? or shoud I generate a series, i dont remember how this statistics work.

JP