SOLUTION: I am so confused...need help please! Determine which two equations represent perpendicular lines. (a) y=2x-9 (b) y=1/2x+9 (c)y=-1/2x+9 (d) y=1/2x-9

Algebra ->  Equations -> SOLUTION: I am so confused...need help please! Determine which two equations represent perpendicular lines. (a) y=2x-9 (b) y=1/2x+9 (c)y=-1/2x+9 (d) y=1/2x-9       Log On


   

Question 73809: I am so confused...need help please!
Determine which two equations represent perpendicular lines. (a) y=2x-9 (b) y=1/2x+9 (c)y=-1/2x+9 (d) y=1/2x-9
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
First, you have to know that given an equation that looks like
y+=+m%2Ax+%2B+b, the slope is m. The equations that you
are given are all in that form. You can read off the slope in each case.
(a) m+=+2
(b) m+=+1%2F2
(c) m+=+-1%2F2
(d) m+=+1%2F2
The slopes are all you care about. Forget the b.
Now all you have to know is that if you have 2 lines
and m%5B1%5D+=+m%5B2%5D, then the lines are parallel
If m%5B1%5D+=+-%281%2Fm%5B2%5D%29, then the lines are perpendicular
I see right away that (b) and (d) are parallel
And I see that (a) and (c) are perpendicular because
m%5B1%5D+=+-%281%2Fm%5B2%5D%29 when m%5B1%5D+=+2 and m%5B2%5D+=+-1%2F2