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Elenadan62p4rq7k
a fost răspuns

b=2+4+6+...100
b=?
c=3+6+9+...2010
c=?
d=5+10+15+...+2015
d=?
e=18+28+38+...+308
e=?
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Răspuns :

Gabygabytzzu

b=2+4+6+...+100=2(1+2+3+...+50)=2×50×51/2=50×51=2550

c=3+6+9+...+2010=3(1+2+3+...670)=3×670×671/2=674335

d=5+10+15+...+2015=5(1+2+3+...+403)=5×403×404/2=407030

e=18+28+38+...+308=10+8+20+8+...+300+8=10(1+2+3+...+30)+8×30=10×30×31/2 + 240=4650+240=4890

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