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aflati numarul natural x daca 3+6+9+.....+297=150 x

Răspuns :

3+6+9+...+297=150x
3( 1+2+3+...+99 )=150x | :3
1+2+3+...+99=50x
(99*100):2=50x ^^^
99*100=100x
x=99

^^^ Se rezolvă cu suma lui Gauss : 1+2+3+...+n=[n(n+1)]:2
3+6+9+...+297=150x
3( 1+2+3+...+99 )=150x | :3
1+2+3+...+99=50x
(99*100):2=50x ^^^
99*100=100x
x=99