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Andreea1340
a fost răspuns

calculati:a)4+8+12+...+28;b)25+26+27+...44

Răspuns :

DeeeaFlorina
a) 4+8+12+...+28=
=4×(1+2+3+...+7)
=4×28×(28+1):2
=4×28×29:2
=2×28×29
=56×29
=1624

b) S=25+26+27+....+44
S=44+43+42+....+25
___________________
2×S=69+69+69+...+69
(44-25):1+1=19:1+1=19+1=20 termeni

2×S=69×20
S=69×20:2
S=69×10
S=690

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