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Calculati :
\frac{43}{5} + \frac{45}{5} + \frac{47}{5} + ... + \frac{97}{5} =
Dau coroana


Răspuns :

(1/5)*(43+45+47+.....+93+95+97)

43+45+47+.....+93+95+97=(43+97)+(45+95)+...+140
cate perechide 140 avem?
avem (97-43)/2 +1=54/2+1=27+1=28 perechi

altfel
43=2*21+1
97=2*48+1
de la 21 la 48 sunt 48-21+1=27+1=28 numere

deci suma este (1/5)*140*28=28*28=784