1. The problem statement, all variables and given/known data An LC circuit consists of a 1mH inductor. The capacitor is fully charged. After 2.1 ms, the energy in the capacitor is ½ of its original value. What is the capacitance of the circuit? 2. Relevant equations (Q/C)+ L(d^2Q/dt^2)=0 d^2Q/dt^2= -(1/LC)Q 3. The attempt at a solution I found the above equations in my physics book but I don't know what Q would be (it says that the capacitor is fully charged but it doesn't give an actual number), or how to get into a C= ? format in order to find the capacitance. Also I'm not even sure these are the formulas I need for this problem and if they're not then I have no idea what to do.