Question

Calculați urmatoarele sume 1+2+3+-+30; 6 2+3+4+...+30; 9+10+11+...+30.*Va rog ,urgent *! DAU COROANA !-MULȚUMESC !​

Answer 1

Răspuns:

$\frac{(1 + 30) \times 30}{2} = \frac{31 \times 30}{ 2} = 31 \times 15 = 465$

$\frac{(2 + 30) \times 29}{2} = \frac{32 \times 29}{2} = 16 \times 29 = 464$

$\frac{(9 + 30) \times 22}{2} = \frac{39 \times 22}{2} = 39 \times 11 = 429$