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:${\frac {d{\boldsymbol {v}}(t)}{d{\mathit {t}}}}={\boldsymbol {a}}(t)$

or
:${\boldsymbol {v}}(t)={\boldsymbol {v}}(t_{0})+\int _{t_{0}}^{t}{\boldsymbol {a}}(t')\ d{\mathit {t'}}$