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Calculeaza:
a)2+4+6+...+158=?
b)3+6+9+...+162=?
c) 4+8+12+...+288=?
d) 7+14+21+...+147=?



Răspuns :

a)160×79:2=80×79
b)165×52:2=165×26
c)292×72:2=292×36
d)154×21:2=77×21
a)2(1+2+3...+79)=2*79(79+1)/2=2*79*80/2=79*80=6320
b)3(1+2+3...+54)=3*54(54+1)/2=3*54*55/2=4455
c)4*72*73/2=10512
d)7*21*22/2=1617