(OSEC) Simplificando-se $\phantom{X}\dfrac{\;[(n\,-\,1)!]^2\,+\,(n\,-\,1)!n!\,+\,(n\,-\,1)!n!\,+\,(n!)^2\;}{(n\,-\,1)!\,+\,n!\,+\,(n\,+\,1)!}\phantom{X}$ obtém-se:
b)
$\,(n\,+\,1)!\,\phantom{\dfrac{X}{X}}$
d)
$\,\dfrac{\;n!(n\,-\,1)!\;}{(n\,+\,1)!}\,$
e)
$\,\dfrac{\;(n\,-\,1)!\;}{(n\,+\,1)!}\,$