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S=(1+2+3+4+...+89)+(7+14+21+...+420)​

Răspuns :

Răspuns:

S=[89·(89+1)]/2 + 7(1+2+3+...+60)

S=4005+7·[60·(60+1)]/2

S=4005+7·3660

S=4005+25620

S=29625