Răspuns:
[tex]a = 1 + 2 + 3 + ... + 11 = \frac{((11 - 1) \div 1 + 1) \times (1 + 11)}{2} = \frac{10 \times 12}{2} = \frac{120}{2} = 60[/tex]
[tex]b =9 + 10 + 11 + ... + 18 = \frac{((18 - 9) \div 1 + 1) \times (9 + 18)}{2} = \frac{10 \times 27}{2} = \frac{270}{2} = 135[/tex]
a+b=60+135=195
