It is currently 18 Nov 2017, 22:10

Close

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Close

Request Expert Reply

Confirm Cancel

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

M23 Q14

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
Tuck Thread Master
User avatar
Joined: 20 Aug 2009
Posts: 305

Kudos [?]: 165 [0], given: 69

Location: Tbilisi, Georgia
Schools: Stanford (in), Tuck (WL), Wharton (ding), Cornell (in)
M23 Q14 [#permalink]

Show Tags

New post 23 Feb 2010, 12:57
I want to discuss following question:

If line \(y = kx + b\) is parallel to line \(x = b + ky\) , which of the following must be true?

A) \(k = b\)
B) \(k = 1\)
C) \(b + k = 0\)
D) \(|k| - 1 = 0\)
E) \(k = -k\)


[Reveal] Spoiler: OA:
D


[Reveal] Spoiler: OE:
For lines to be parallel, their slopes must be equal. The second equation can be rewritten as \(y = \frac{1}{k}*x - \frac{b}{k}\) . Because slopes must be equal, \(k = \frac{1}{k}\) or \(k^2 = 1\) or \(|k| = 1\) .



Obviously the slopes of the lines should be the same. But what about y-intercepts? If the slopes of two lines are same AND y-intercepts are also the same we in fact have the same line, not two parallel lines.

From equality of slopes we establish, that \(|k|=1\), but I also thought that maybe -
\(b\neq-\frac{b}{k}\)
\(k\neq-1\)
\(k=1\)

What do you think?

Kudos [?]: 165 [0], given: 69

Manager
Manager
User avatar
Joined: 13 Dec 2009
Posts: 248

Kudos [?]: 256 [0], given: 13

Reviews Badge
Re: M23 Q14 [#permalink]

Show Tags

New post 13 Mar 2010, 11:58
shalva wrote:
I want to discuss following question:

If line \(y = kx + b\) is parallel to line \(x = b + ky\) , which of the following must be true?

A) \(k = b\)
B) \(k = 1\)
C) \(b + k = 0\)
D) \(|k| - 1 = 0\)
E) \(k = -k\)


[Reveal] Spoiler: OA:
D


[Reveal] Spoiler: OE:
For lines to be parallel, their slopes must be equal. The second equation can be rewritten as \(y = \frac{1}{k}*x - \frac{b}{k}\) . Because slopes must be equal, \(k = \frac{1}{k}\) or \(k^2 = 1\) or \(|k| = 1\) .



Obviously the slopes of the lines should be the same. But what about y-intercepts? If the slopes of two lines are same AND y-intercepts are also the same we in fact have the same line, not two parallel lines.

From equality of slopes we establish, that \(|k|=1\), but I also thought that maybe -
\(b\neq-\frac{b}{k}\)
\(k\neq-1\)
\(k=1\)

What do you think?


It should be D, cos y intercept can be equal as it is given that lines are parallel but it is not given that lines are not equal.
_________________

My debrief: done-and-dusted-730-q49-v40

Kudos [?]: 256 [0], given: 13

Re: M23 Q14   [#permalink] 13 Mar 2010, 11:58
Display posts from previous: Sort by

M23 Q14

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  

Moderator: Bunuel



GMAT Club MBA Forum Home| About| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.