1. The problem statement, all variables and given/known data The force exerted by an unusual spring when it's compressed a distance 20cm from equilibrium is given by F= -kx-cx3, where k= 233 N/m and c= 4.0kN/m3 Question: Find the energy stored in this spring when it's been compressed 20cm. 2. Relevant equations Equation already given, I think we supposed to use that one. But the equation of spring constant is Us= (1/2)kx02-(1/2)kxf2. 3. The attempt at a solution. I actually just put in the right numbers in the equation given, but was incorrect. Did integrate the function, and was wrong. No clue what to do.