In damped SHM, how do we know the motion has a single constant frequency throughout — without assuming it from the start? – physics.stackexchange.com

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In damped SHM, we write: $$m\ddot{x} + b\dot{x} + kx = 0$$ The standard approach assumes a solution of the form $e^{\alpha t}$ and derives: $$\omega_d = \sqrt{\frac{k}{m} - \frac{b^2}{4m^2}}.$$ But ...