Question

4+8+12+......+1996
calculati sumele.

Answer 1

factor comun 4
4(1+2+3+4+.......+499)=
la paranteza suma lui Gauss
S=[(1+499)*499]/2=(500*499)/2=250*499=124750
revenim si inmultim cu 4
4*124750=499000

Answer 2

$4+8+12+.....+1996=\\4*(1+2+3+.....+499)=\\4*499*(499+1)/2=\\2*499*500=\\499000$