[tex] \frac{1}{1*2} + \frac{1}{2*3} + ... + \frac{1}{24*25} [/tex] =
= [tex][ \frac{1}{1} - \frac{1}{2}] + [\frac{1}{2} - \frac{1}{3}] + ... + [ \frac{1}{24} - \frac{1}{25} ][/tex] Observam ca toti termenii se reduc mai putin [tex][ \frac{1}{1} - \frac{1}{25} ] = \frac{24}{25} [/tex]
