I'm fairly certain you have an error in your equation as the curve you suggests opens upward so has no maximum profit. Profit becomes positive on completion of the 7th unit. (curve crosses x axis at (6.056, 0))
I will GUESS that the equation should read
P(x) = - 2x² + 120x – 800
Maximum will occur when the derivative is zero (zero slope)
False. Two negatives equal a positive. if you say don't do that (negative) and then say don't don't do that (negative) you have said to do it (positive). Truth value means true or false.