Question

calculati urmatoarele sume:
a)S=3+5+7+...+1001-2-4-6-...-1000;
b)S=2+4+6+8+...+668-3-5-7-...-667;
c)S=1+2+3+...2016-1000-1001-...-2016;
d)S=5+10+15+...+200-3-8-13-...198.
             Dau coroana!!

Answer 1

a) S= 3+5+7+...+1001-2-4-6-...-1000=
= 3-2+5-4+7-6+...+1001-1000=
=1+1+1+...+1 (de 1000 de ori) =
=1× 1000=
=1000
b) S= 2+4+6+8+...+668-3-5-7-...-667 =
= 2+ 4-3 + 6-5 + .... +668-667 =
= 2+ 1+1+...+1 (de 667 de ori) =
= 2+ 1×667 =
= 669
c) S= 1+2+3+...+2016-1000-1001-...-2016
= 1+2+3+... + 999 (de la 1000 la 2016 se scad)
= 999×1000 : 2 =
= 999×500 =
= 499500
d) S= 5+10+15+...+200-3-8-13-...-198
= 5-3 + 10-8 + 15-13 + ... + 200-198=
= 2+2+2+...+2 (de 40 de ori) =
= 2× 40 =
= 80
Sper ca te-am ajutat si ca ai inteles