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15+16+17.......+120=??? Va rog coroana

Răspuns :

Alexandra1079
15+16+17+...+120=
120-14=106 nr in sir

15+16+17+...+120=
120+119+118+...+15=
2S=135+135+135+...+135+135=
2S=135×106
S=(135×106):2
S=7155
15+16+17...120=7155
Sper că te-am ajutat!

(1+2+3+............+120)-(1+2+3+..............+14)

[(120x121):2]-[(14x15):2]

(60x121)-(7x15)

7260-105

7155

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