[Tex/LaTex] How to write the equations with conditions in two lines

Question

I want to write the boundary condition in the following form. Need your help to write the below equations in two lines

Answer 1

You really want to use alignat or alignedat (the difference being that the former types two equations, the latter one equation on two lines)

\documentclass{amsart}
\begin{document}
  \begin{alignat}{8}
    \nu &= V_w &&= cz/l, & \qquad u&= U_0, &\qquad \text{at\quad} r &=R, \\
    \nu &\rightarrow V_e &&= az/l, &\qquad T &\rightarrow T_{\infty},&\qquad \text{as\quad} r &\rightarrow \infty,
  \end{alignat}

  \begin{equation}
    \begin{alignedat}{8}
      \nu &= V_w &&= cz/l, & \qquad u&= U_0, &\qquad \text{at\quad} r &=R, \\
      \nu &\rightarrow V_e &&= az/l, &\qquad T &\rightarrow T_{\infty},&\qquad \text{as\quad} r &\rightarrow \infty,
    \end{alignedat}
  \end{equation}

  \begin{equation*}
    \begin{alignedat}{8}
      \nu &= V_w &&= cz/l, & \qquad u&= U_0, &\qquad \text{at\quad} r &=R, \\
      \nu &\rightarrow V_e &&= az/l, &\qquad T &\rightarrow T_{\infty},&\qquad \text{as\quad} r &\rightarrow \infty,
    \end{alignedat}
  \end{equation*}

\end{document}

both environments are found in amsmath , which is loaded by amsart in my mwe