Respostas

2014-06-22T10:28:32-03:00
  \left[\begin{array}{ccc}x&y&1\\x_a&y_a&1\\x_b&y_b&1\end{array}\right]

Fazendo o Determinante temos:

  \left[\begin{array}{ccc}x&y&1\\-1&0&1\\2&-1&1\end{array}\right]   \begin{array}{ccc}x&y&\\-1&0&\\2&-1&\end{array}\right]

0+x+y+0+2y+1=0
3y=-x-1
y= \frac{-x-1}{3} ou y= \frac{-x}{3} - \frac{1}{3}

Coeficiente Angular:  \frac{-1}{3}
Coeficiente Linear:  \frac{-1}{3}
2 3 2