[tex] b_{n+1}- b_{n}= [-3(n+1)-1]-(-3n-1)=-3n-3-1+3n+1 =-3[/tex]
Deci [tex] b_{n+1}- b_{n}\ \textless \ 0,adica, b_{n+1}\ \textless \ b_{n} [/tex], inlocuind pe n cu valorile 1,2,3,...,n, obtinem: [tex] b_{1}\ \textgreater \ b_{2}\ \textgreater \ b_{3}\ \textgreater \ ...\ \textgreater \ b_{n}\ \textgreater \ b_{n+1}\ \textgreater \ ... [/tex], deci este descrescator.
