Answer:
First, write the alternate series as [tex]\sum_{ n = 1 }^{\infty } (-1)^{n} a_n[/tex] where the term [tex]a_n[/tex] is positive. From the Cauchy criterion we already know that [tex]a_n\rightarrow 0[/tex]. So, in order to assure the convergence we only need to ask that the term [tex]a_n[/tex] is monotonically decreasing.
Step-by-step explanation:
This is the Leibniz criterion for the convergence of alternate series.