Command/startformula

This is the first mathematical formula
 \placeformula[First]
 \startformula
   \sin^2(t)^2 + \cos^2(t) = 1.
 \stopformula

This is another formula
 \placeformula[eqn:tangent]
 \startformula
   \cos^2(t) = \frac{1}{1+\tan^2(t)}.
 \stopformula
As one may see from relation~(\in[eqn:tangent]), $\cos(t)$ and
$\sin(t)$ can be determined by $\tan(t)$\dots

This is the third formula
 \placeformula[Pythagora]
 \startformula
    |a+b|^2 = |a|^2 + |b|^2
 \stopformula
Clearly equality (\in[Pythagora]) holds for $a,b \in {\Bbb R}^n$
if and only if $(a|b) =0$, where the scalar product
$(\cdot|\cdot)$ on ${\Bbb R}^n$ is defined to be
 \startformula
   (a|b) := a\cdot b =\sum_{j=1}^{n}a_jb_j, \qquad |a|^2 := (a|a).
 \stopformula
(Note that the above equation is {\it not\/} numbered).