Respostas

2014-07-28T20:59:29-03:00
(2-7x) . (2+7x)=
(2-7x)²=
x=4

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2014-07-28T21:00:48-03:00
(2-7x) . (2+7x)
     5x . 9x
       45x

1 5 1