
\eqalign - Used for equation alignment; for aligning multi-line displays at a single place.
{ \eqalign{ <math> & <math> \cr <repeat as needed> } }
\eqalign command is used for equation alignment; for aligning multi-line displays at a single place. The ampersand is placed where alignment is desired; a double-backslash can be used in place of the \cr ; the final \\ or \cr is optional; supports only a single \tag, which is vertically centered.
\eqalign{
3x - 4y &= 5\cr
x + 7 &= -2y
}
\eqalign{
(a+b)^2 &= (a+b)(a+b) \\
&= a^2 + ab + ba + b^2 \\
&= a^2 + 2ab + b^2
}
\left\{
\eqalign{
a &= 1\\
b &= 2\\
c &= 3
}\right\}
\qquad
\eqalign{
ax + by &= c \\
x + 2y &= 3
}