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3+6+9+...+180=?
rezolvarea


Răspuns :

3 * (1 + 2 + 3 + .......+ 60) = 3 * 60 : 2 * (60 + 1) = 3 * 30 * 61 = 5490
3+6+9+...+180=3(1+2+3+...+60)=3*60*61/2=3*30*61=5490