Solve this problem by educated guessing. Suppose f is the function that satisifes f′′(x)=−f(x) for all x in its domain, f(0)=0, and f′(0)=1. Then f(x)=?

Jessica is organizing a guided tour of the rain forest. the average profit per person that the touring company makes is given by the rational expression 18x+35/x, where x is the number of people going on the tour. what does the numerator of this rational expression represents?