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### Parallel Lines

Date: 9/3/96 at 13:10:58
From: Anonymous
Subject: Parallel Lines

getting anywhere on this question in our textbook.

"The lines y=kx+4 and 3y=(k+3)x-5 are parallel. Find k."

Can you explain how to do it, please? Many thanks.

Emma and Marie.

Date: 9/3/96 at 14:2:48
From: Doctor Mike
Subject: Re: graphs.

You first need to get both line equations is slope-intercept form.
The first one is in that form already. To get the second one in that
form you divide both sides by 3, giving

k+3      5
y  =  --- *x - ---
3       3

For the lines to be parallel the slopes have to be the same, so k must
equal (k+3)/3 , and that is easily solved as k=3/2 .  The two lines
are y=(3/2)x + 4 and y=(3/2)x - (5/3).  Each has the slope 3/2 and
they intersect the y-axis at (0,4) and (0,-(5/3)) .

I hope this helps.  Write back if you have other questions.

-Doctor Mike,  The Math Forum
Check out our web site!  http://mathforum.org/dr.math/

Associated Topics:
Middle School Algebra

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