Assume that the height of your cylinder is 4 inches. Consider A as a function of r , so we can write that as A(r)=2πr2+8πr . What is the domain of A(r) ? In other words, for which values of r is A(r) defined? Part b: Continue to assume that the height of your cylinder is 4 inches. Write the radius r as a function of A . This is the inverse function to A(r) , i.e., to turn A as a function of r into r as a function of A .