Răspuns :
-2-4-6-...-2000=
= -2(1+2+3+...+1000) =
= -2×1000×1001:2 =
= -2×500×1001 =
= -2 × 500500 =
= - 1001000
= -2(1+2+3+...+1000) =
= -2×1000×1001:2 =
= -2×500×1001 =
= -2 × 500500 =
= - 1001000