Translations:The unit tangent vector/2/es

${\begin{aligned}\mathbf {u=} &{\frac {d\mathbf {r} }{ds}}{\rm {=}}{\frac {dx}{ds}}\mathbf {i} +{\frac {dy}{ds}}\mathbf {j} =\left({\frac {dx}{ds}},{\frac {dy}{ds}}\right).\end{aligned}}$

(2)