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17+ 18+ 19+ ... +84 supra 42

Răspuns :

[tex][tex] \frac{(1+2+3+...+84)-(1+2+3+...+16)}{42} \frac{(84*85/2)-(16*17/2)}{42}= \frac{(7140/2)-(272/2)}{42}= [/tex]
[tex] \frac{3570-136}{42}= \frac{3434}{42} [/tex]