1. The problem statement, all variables and given/known data Hello, everyone. :) I'm having trouble with problem 2.26(b) from the attached PDF file. 2. Relevant equations d^2 y/dt^2 = 6Hu^2/L^2 - 12Hxu^2/L^3 d^2 y/dt^2 <= A 6Hu^2/L^2 - 12Hxu^2/L^3 <= A 6Hu^2/L^2 <= A 3. The attempt at a solution I don't understand why the fact that x > 0 means that the term -12Hxu^2/L^3 in d^2 y/dt^2 = 6Hu^2/L^2 - 12Hxu^2/L^3 can be ignored. To me, it seems that removing it makes the inequality go from some_quantity <= A to some_larger_quantity <= A. How does one justify that? Any input would be greatly appreciated!