Question

1+4+7+...+49= Va rog

Answer 1

1+4+7+...+49=
(49-1)/3+1=48:3+1=16+1=17 numere
vom avea  8 grupe de cate 2 (a caror suma este 50 ) si  25
=(1+49)+ (4+46) + ...(+22+28) + 25 = 50*8+25=400+25=425 

Answer 2

=(3*0+1)+(3*1+1)+(3*2+1)+....+(3*16+1)
=3*(1+2+...+16) +17*1
=3[(16*17)/2]+17
=3*136+17
=408+17
=425