maths questions about equation

Let M be the mid point of line BC, then line AM is the median through point A.

The coordinates of M is: [(3+11)/2, (-6-2)/2] = (7,-4)
Now, applying the two point formula (y-y1)/(y2-y1)=(x-x1)/(x2-x1) for the points
A(4,5) and M(7,-4)
Hence the equation for AM will be
(y - 5) / (-4 - 5) = (x - 4) / (7 - 4)
(y - 5) / -9 = (x - 4) / 3
y - 5 = -3x + 12
3x + y = 17

Hence the answer is: 3x + y - 17 = 0


2011-10-06 20:20:35 補充：
y = -3x + 17