To answer Section 1.2, number 17, if you don't have a graphing calculator, you can get a fair idea of what's going on by going to this website: Javascript Function Evaluatory. If you fill in the boxes the way I have, below, you will get a nifty graph of the function that DOES suggest a low point, somewhere in the vicinity of (420, 300), which I have displayed on the right.
I filled in the x-values (airspeeds) in the table, clicked "Evaluate" and the Evaluator filled in the y-values (the cost per passenger).
You could play around with the gridlines to zero-in on the low point. (an inefficient graphing approach)
You can do a a guess-and-check in the neighborhood of x = 420, to find the low point on the cost function, also. (an inefficient numerical approach)
You could also keep changing the Xmin, Xmax, Ymin, and Ymax to get a window that zeroed-in on the apparent low point. It's time-consuming, but you can eventually get a window that's smaller than the degree of accuracy required for the answer. (another inefficient graphing approach).
Any decent graphing calculator has a "Find the Min" function built in...
You could zero in better with a good graphing calculator. But this website is a good place for building a table of values if you don't already have access to a graphing calculator with a Table feature. They cost about $100 in the bookstore (TI-83 or TI-84 are standard types). There are also other free graphers that you can find by google/yahoo searches, if you have some patience.
As it stands, I'm MORE than happy to make this exercise a bonus problem. There are probably quite a few of you who already know from high school how to use a graphing calculator to CLOBBER this kind of problem, but it depends on where and when you went to school. I try to weed these problems out of the exercises, for those who don't "come equipped" with graphing capabilities, but when one slips through, this is how I handle it.
Finding the value of x that minimizes the cost C is a standard graphing calculator task, taught to MANY, but NOT ALL.