Question

Calculati: 6+12+18+...+246=

Answer 1

dam factor comun
6(1+2+3+...+41)

Gauss in paranteza

41*42/2=  
6*41*42/2  simplificam 6 cu 2=
3*41*42=5166

Answer 2

$\displaystyle 6+12+18+...+246=6(1+2+3+...+41)=6 \times \frac{41(41+2)}{2} = \\ \\ =6 \times \frac{41 \times 42}{2} =6 \times \frac{1722}{2} =6 \times 861=5166$