1. The problem statement, all variables and given/known data a) For what nonzero values of k does the function y = sin kt satisfy the differential equation y" + 9y = 0? b) For those values of k, verify that every member of the family of functions y = A*sin kt + B*cos kt is also a solution. 2. Relevant equations 3. The attempt at a solution I'm a little confused on what I need to do here. I can do problems where you have to show that every member of a family of functions is a solution of a differential equation (differentiate the function, then plug in the function into the differential equation, and see if they are the same). But I don't see how to use that in this problem. Thanks for the help.