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Renatafolfa
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Efectuați (3+6+9+.....+30)-(2+4+6+......+20)

Răspuns :

Ancuța2015
3•(1+2+3+...+10)-2•(1+2+3+...+10)=3•11•10:2-2•11•10:2=33•5-22•5=55
(3+6+9+.....+30)-(2+4+6+.....+20)=
=3(1+2+3+....+10)-2(1+2+3+....+10)=
=3x10x11:2-2x10x11:2=
=30x11:2-10x11=
=15x11-10x11=
=11(15-10)=
=11x5=55

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