SOLUTION: If the lines mx + 3y =1 and 3x + (m− 4) y = 5 are perpendicular. Find m.

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Question 1004023: If the lines mx + 3y =1 and 3x + (m− 4) y = 5 are perpendicular. Find m.
Answer by fractalier(6550) About Me  (Show Source):
You can put this solution on YOUR website!
Solve both for y...this will get us the slope for each...we'll set their product equal to -1 to find m...
mx + 3y = 1
3y = -mx + 1
y = (-m/3)x + 1/3
and the other
3x + (m-4)y = 5
(m-4)y = -3x + 5
y = (-3/(m-4)) + 5/(m-4)
so that
(-m/3)(-3/(m-4)) = -1
and
m/(m-4) = -1
m = -m + 4
2m = 4
m = 2