👤

21+42+56+...+1890; dati factor comun si calculati

Răspuns :

21+42+63+...+1890 =

21 × ( 1 + 2 + 3 + ...+ 90) =

21 × 90 × (90 + 1) : 2 =

21 × 45 × 91 =

945 × 91 =

85 995
_______
_______