Răspuns:
f(1)=-1+3=2
f(2)=-2+3=1
f(3)=-3+3=0
'
f50)=-50+3=-47
2+1+0+...+(-47)
3+...-(1+2+3+...47)
1+2+3+...+47=47×48:2=1128
1128+3=1131
