The figure represents the measured displacement-time relationship for a vibration with small damping where it is impractical

Question:

The figure represents the measured displacement-time relationship for a vibration with small damping where it is impractical to achieve accurate results by measuring the nearly equal amplitudes of two successive cycles. Modify the expression for the viscous damping factor ζ based on the measured amplitudes x₀ and x_N which are N cycles apart.