When I write a really large expression in latex, it usually comes in the next line. Like this, $$\alpha\beta=(\frac ab+\frac cd)(\frac bc +\frac da)=\frac ac+\frac bd+\frac db+\frac ca=8 $$ But sometimes out of the blue, instead of going to the next line, it remains in a single line and a bar app...