SOLUTION: Here is the question. Find k if the lines 3x-y=9 and kx+3y=5 are perpendicular. I arranged both equations to equal y; y=3x-9 and y=(5-kx)/3, but I don't know where to go from there

Algebra ->  Graphs -> SOLUTION: Here is the question. Find k if the lines 3x-y=9 and kx+3y=5 are perpendicular. I arranged both equations to equal y; y=3x-9 and y=(5-kx)/3, but I don't know where to go from there      Log On


   

Question 211350: Here is the question. Find k if the lines 3x-y=9 and kx+3y=5 are perpendicular. I arranged both equations to equal y; y=3x-9 and y=(5-kx)/3, but I don't know where to go from there
Answer by checkley77(12844) About Me  (Show Source):
You can put this solution on YOUR website!
3x-y=9
-y=-3x+9
y=3x+9 ( red line)this line has a slope of 3.
Therefore all perpendicular lines will have a slope=-1/3
kx+3y=5
3y=-kx+5
y=-kx/3+5/3
[-k/3=-1/3]
k=1 ans.
y=-x/3+5/3 (green line)
+graph%28+200%2C+200%2C+-10%2C+10%2C+-10%2C+10%2C+3x+%2B9%2C+-x%2F3+%2B5%2F3%29+ (graph 200x200 pixels, x from -10 to 10, y from -10 to 10, of TWO functions 3x +9 and -x/3 +5/3).