Question

(7+14+21+...+1400):(1+2+3+...+20) dau coroana va rog​

Answer 1

$(7 + 14 + 21 + ... + 1400) : (1 + 2 + 3 + ... + 20) \\ \\ = 7(1 + 2 + 3 + ... + 200 ):(1 + 2 + 3 + ... + 20) \\ \\ = 7 \times \frac{200 \times 201}{2} : \frac{20 \times 21}{2} \\ \\ = 7 \times 100 \times 201 : 10 \times 21 \\ \\ = 7 \times 10 \times 201 \times 21 \\ \\ = 70 \times 201 \times 21 \\ \\ = 14070 \times 21 \\ \\ = 295470 \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ formula \: \: \: sumei \: \: \: gauss : \\\boxed{ 1 + 2 + 3 + ... + n = \frac{n(n + 1)}{2} } \\ \\ \\ Sper \: \: că\: \: te-am \: \: ajutat\: !\: ♥︎$