Question

Calculează: a)1+2+3+...+356; b)1+2+3+...+525; c)2+4+6+8+...+500 d)3+6+9+12+...900.

Answer 1

aplici formula n(n+1)/2 daca ai 1+2+3+...+n;
la c) scrii 2(1+2+3+4+..+250) si aplici formula in paranteza;
la d) scrii 3(1+2+3+...+300 si la fel aplici formula in paranteza;

Answer 2

 )a)n*(n+1)/2    357*356/2=357*178=63546 b)525*526/2=525*263=138075 c)  2(1+2+3+4+....+250)=2*251*250/2=2*251*125=62750 d)3(1+2+3+4+...+300)=3*301*300/2=3*301*150=903*150=135450