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2014-10-08T17:15:30+03:00
1. ab+ac=a(b+c)=7*15=105 si ab-ac=a(b-c)=7*7=49
2. ab+ac+ad=a(b+c+d)=7*70=490
3. 3a+2(ab+ac+ad)=9+2a(b+c+d)=9+6*30=9+180=189
2014-10-08T17:18:36+03:00
 ab+ac=ax(b+c)=7x15=105 => axb-axc=ax(b-c)=> 7x7=49
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