Răspuns:
[tex] \frac{1}{3 \times 7} + \frac{1}{7 \times 11} + \frac{1}{11 \times 15} + \frac{1}{15 \times 19} = [/tex]
[tex] { \frac{1}{21} }^{(1045} + { \frac{1}{77} }^{(285} + { \frac{1}{165} }^{(133} + { \frac{1}{285} }^{(77} = [/tex]
[tex] \frac{1054 + 285 + 133 + 77}{21945} = [/tex]
[tex] { \frac{1540}{21945} }^{(385} = [/tex]
[tex] = \frac{4}{57} [/tex]
