Processing math: 33%
x(u,v)=3cosusinv,y(u,v)=3sinusinv,z(u,v)=3(cosv+ln(tan(v2)))+u4
x(u,v)=ucosv,y(u,v)=usinv,z(u,v)=u/3
\begin{align*} x(u,v) &= (3 + \cos u)\cos v, \\ y(u,v) &= (3 + \cos u)\sin v, \\ z(u,v) &= \sin u \end{align*}
\begin{align*} x(u,v) &= (1 + \tfrac{1}{5}\sin(5u)\sin(5v))\sin v\cos u, \\ y(u,v) &= (1 + \tfrac{1}{5}\sin(5u)\sin(5v))\sin v\sin u, \\ z(u,v) &= (1 + \tfrac{1}{5}\sin(5u)\sin(5v))\cos v \end{align*}
\begin{align*} x(u,v) &= (1+\dfrac{v}{2}\cos\dfrac{u}{2})\cos u, \\ y(u,v) &= (1+\dfrac{v}{2}\cos\dfrac{u}{2})\sin u, \\ z(u,v) &= \dfrac{v}{2}\sin\dfrac{u}{2} \end{align*}
\begin{align*} x(u,v) &= u(1-u^2/3+v^2)/2, \\ y(u,v) &= -v(1-v^2/3+u^2)/2, \\ z(u,v) &= (u^2-v^2)/2 \end{align*}