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Calculati:
  1.   S  = 1+2+3................+600=
   2.   S =51+52+53.............+600=
  3.   S = 3+6+9.................+600=


Răspuns :

1. S = 1+2+3................+600=
=600*601:2=
=180 300

2. S =51+52+53.............+600=
=(  600+51)(600-51+1):2=
=651*550:2=
=179 025

3. S = 3+6+9.................+600=
=(600+3)[(600-3):3+1]:2=
=603*200:2=
=60 300