A particle of mass \(m\) is constrained to move along the \(x\)-axis in a region where its potential energy is given by \(U(x) = U_0 \tan^2(\alpha x)\), where \(U_0\) and \(\alpha\) are positive constants and \(-\dfrac{\pi}{2\alpha} < x < \dfrac{\pi}{2\alpha}\). Which of the following expressions correctly gives the acceleration \(a(x)\) of the particle as a function of position \(x\)?