You have never been able to use \\
in the equation
environment. The usage of it in that environment has always produced errors, because equation
can just contain one line. An exception is the usage of internal auxiliary environments such as split
, aligned
or alignedat
, but in this case \\
would not be in the equation
environment, but in the auxiliary one.
Load amsmath
with \usepackage{amsmath}
in any document that has math.
If you want to display two consecutive equations as if each is in equation
, then use gather
:
\begin{gather}
\cosh^{2} t - \sinh^{2} t = 1 \\
2\sinh^{2} t + 1 = \sinh 2t
\end{gather}
If you want to highlight the equals signs, use align
:
\begin{align}
2\sinh t &= e^{t}-e^{-t} \\
2\cosh t &= e^{t}+e^{-t}
\end{align}
Note: MathJax allows using \\
in equation
or \[...\]
. I think this is a bad mistake, because it makes for unportable code.
align
,gather
,multine
and the like.equation
is not designed to do it!amsmath
multi-line structures are built in essentially the same way.equation
is different because it is defined essentially the same as in basic latex; only a*
form has been added.\\
inequation
, which can be grossly misleading to its users when they switch to proper LaTeX.