\(\frac{\mathrm{dt}}{\mathrm{dx}}=2 \alpha \mathrm{x}+\beta\)
\(\frac{1}{\mathrm{v}}=2 \alpha \mathrm{x}+\beta\)
\(\text { (differentiating wrt time) }\)
\(-\frac{1}{\mathrm{v}^2} \frac{\mathrm{dv}}{\mathrm{dt}}=2 \alpha \frac{\mathrm{dx}}{\mathrm{dt}}\)
\(\frac{\mathrm{dv}}{\mathrm{dt}}=-2 \alpha \mathrm{v}^3\)