Respuesta :

[tex]\left\|\dfrac{\partial(x,y)}{\partial(s,t)}\right\|=\left|\begin{vmatrix}\dfrac{\partial x}{\partial s}&\dfrac{\partial x}{\partial t}\\\\\dfrac{\partial y}{\partial s}&\dfrac{\partial y}{\partial t}\end{vmatrix}\right|=\left|\begin{vmatrix}1&5\\3&8\end{vmatrix}\right|=|-7|=7[/tex]