Exercise 16. Evaluate J sin (x) cos(x) dx. Use the substitution u = sin(x). Why is this a good choice? What would other choices give? Exercise 17. Evaluate ( sin"(x) cos(x) dx, where a can be any real number at all. Exercise 18. Evaluate f sin*(x) cos(x) dx. Why is using cos?(x) = 1 - sin (x) an emi- nently sensible thing to do here? How does that reduce things to the previous exercise