calculează
[tex]2( \frac{1}{1 \times 2} + \frac{1}{2 \times 3} + \frac{1}{3 \times 4} + ... + \frac{1}{2018.2019} + \frac{1}{2019 \times 2020} [/tex]
totul supra
[tex] \frac{1}{1 + 2 + 3 + 4 + ... + 2018 + 2019} [/tex]
va rog repede dau coroana ​