Folosind formula:
[tex]\it \dfrac{1}{k(k+1)}=\dfrac{1}{k}-\dfrac{1}{k+1}[/tex]
suma dată se scrie:
[tex]\it S=\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\ ...\ +\dfrac{1}{92}-\dfrac{1}{93}=\dfrac{^{31)}1}{\ 3}-\dfrac{1}{93}=\dfrac{31-1}{93}=\dfrac{30^{(3}}{93}=\dfrac{10}{31}[/tex]
