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9+6×[7+5×(5+2×a)]=681




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Răspuns :

9+6×[7+5×(5+2×a)]=681
6×[7+5×(5-2×a)]=681-9
6×[7+5×(5-2×a)]=672
7+5×(5-2×a)=672÷6
7+5×(5-2×a)=112
5×(5+2×a)=112-7
5×(5-2×a)=105
5-2×a=105÷5
5-2×a=21
2×a=21-5
2×a=16
a=16÷2
a=8

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