Help/Adv. Equations

Multiple Lines in Equations

Multiple lines in equations are handled between the delimiters \ begin{align} and \ end{align} with each line separated from the next with the use of '\\' at the end. Each line can be aligned at a location designated by '&' on each line.

For example, that the equation: \begin{align} & \text{if} \quad r\le 1.57\quad {{f}_{w}}=0.3 \\ & \text{if} \quad r>1.57\quad {{f}_{w}}=0.00251\ \exp \left( 5.21\ {{r}^{-0.19}} \right) \\ \end{align}

was typed as follows:
\ begin{align}
   & \text{if} \quad r\le 1.57\quad {{f}_{w}}=0.3 \\
   & \text{if} \quad r>1.57\quad {{f}_{w}}=0.00251\ \exp \left( 5.21\ {{r}^{-0.19}} \right) \\
\ end{align}

The same multi-line equation can be numbered, by enclosing the whole of the "align" inside a "equation" class, as shown below: \begin{equation} \tag{25} \begin{align} & \text{if} \quad r\le 1.57\quad {{f}_{w}}=0.3 \\ & \text{if} \quad r>1.57\quad {{f}_{w}}=0.00251\ \exp \left( 5.21\ {{r}^{-0.19}} \right) \\ \end{align} \end{equation}

was typed as follows:
\ begin{equation} \tag{25}
\ begin{align}
   & \text{if} \quad r\le 1.57\quad {{f}_{w}}=0.3 \\
   & \text{if} \quad r>1.57\quad {{f}_{w}}=0.00251\ \exp \left( 5.21\ {{r}^{-0.19}} \right) \\
\ end{align}
\ end{equation}