Resposta :
-2 | 1 | -1 | a | 7
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| 1 | -3 | 6+a | -12-2a+7
-12-2a+7=0
-5 = 2a
a=-5/2
---------------------------------
| 1 | -3 | 6+a | -12-2a+7
-12-2a+7=0
-5 = 2a
a=-5/2