1. The problem statement, all variables and given/known data Trying to go over this part of my test review. I'm not understanding how to do this. The specific problem which I actually have worked out in my notes: A diff equation model of the motion of a spring where x is displacement from the spring's natural length, k is the spring constant, and m is the mass as follows: (d^2*x)/(d*t^2) = k/m * x Show that x(t)=sin(sqrt(k/m)*t) + 2cos(sqrt(k/m)*t) is a solution to the model. 3. The attempt at a solution My notes appear to take the first, then the second dir. of the second function there. But thats all I can make sense of. Maybe I'm not understanding how to take the dir of these functions I'm not sure. For example on the second to the last line, how am I supposed to simplify -k/m (sin(sqrt(k/m)t) + 2cos (sqrt(k/m)t) to -k/mx thanks for any help!