100+2x100+3x100+....+49x100

Răspuns :

100x(1+2+3.....+49)
100x 49×50/5
100×49×25
100+2·100+3·100+....+49·100= dam termen comun
=100(1+2+...+49)  in paranteza avem acum o suma de tip Gauss
=100(49
·50:2)
=122500