GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 23 May 2019, 16:05

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

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

Which of the following points is reflect to y=-x at (-2,1)?

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics
Author Message
TAGS:

Hide Tags

Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 7367
GMAT 1: 760 Q51 V42
GPA: 3.82
Which of the following points is reflect to y=-x at (-2,1)?  [#permalink]

Show Tags

06 Jan 2017, 02:45
1
6
00:00

Difficulty:

45% (medium)

Question Stats:

58% (01:23) correct 42% (01:13) wrong based on 167 sessions

HideShow timer Statistics

Which of the following points is reflect to y=-x at (-2,1)?

A. (-1, 2) B. (1,-2) C. (2,1) D. (2,-1) E. (1,2)

_________________
MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only \$149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"
Intern
Joined: 04 Jan 2017
Posts: 9
Re: Which of the following points is reflect to y=-x at (-2,1)?  [#permalink]

Show Tags

06 Jan 2017, 09:20
2
Y=-x is a line in second quadrant.
And point (-2,1) lies below it so its reflection to y=-× will be opposite but in the same quadrant .
So D

Sent from my SM-G610F using GMAT Club Forum mobile app
Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 7367
GMAT 1: 760 Q51 V42
GPA: 3.82
Re: Which of the following points is reflect to y=-x at (-2,1)?  [#permalink]

Show Tags

08 Jan 2017, 18:12
1
2
==> You can figure out a point reflecting to y=-x by substituting –y to x-coordinate and –x to y-coordinate. Then, (-2,1) --> (-1, -(-2))=(-1,2) is derived.

Hence, the answer is A.
_________________
MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only \$149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"
Target Test Prep Representative
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 6207
Location: United States (CA)
Re: Which of the following points is reflect to y=-x at (-2,1)?  [#permalink]

Show Tags

09 Jan 2017, 10:37
2
2
MathRevolution wrote:
Which of the following points is reflect to y=-x at (-2,1)?

A. (-1, 2) B. (1,-2) C. (2,1) D. (2,-1) E. (1,2)

When reflecting a point across the line y = -x, we can follow this rule:

If coordinates (a,b) are reflected across the line y = -x, then the new reflected coordinates are (-b, -a).

Thus, when (-2,1) is reflected across the line y = -x, the new reflected coordinates are (-1,2).

_________________

Scott Woodbury-Stewart

Founder and CEO

Scott@TargetTestPrep.com
122 Reviews

5-star rated online GMAT quant
self study course

See why Target Test Prep is the top rated GMAT quant course on GMAT Club. Read Our Reviews

If you find one of my posts helpful, please take a moment to click on the "Kudos" button.

Director
Joined: 12 Nov 2016
Posts: 725
Location: United States
Schools: Yale '18
GMAT 1: 650 Q43 V37
GRE 1: Q157 V158
GPA: 2.66
Re: Which of the following points is reflect to y=-x at (-2,1)?  [#permalink]

Show Tags

20 Feb 2017, 19:23
Which of the following points is reflect to y=-x at (-2,1)?

A. (-1, 2) B. (1,-2) C. (2,1) D. (2,-1) E. (1,2)

Okay so I think "C" is the trap answer in this question. (2,1) reflects (-2,1) but we're dealing with y= "-x"
Manager
Joined: 19 Jul 2017
Posts: 85
Location: India
Concentration: General Management, Strategy
GPA: 3.5
Re: Which of the following points is reflect to y=-x at (-2,1)?  [#permalink]

Show Tags

02 Sep 2017, 08:34
MathRevolution wrote:
Which of the following points is reflect to y=-x at (-2,1)?

A. (-1, 2) B. (1,-2) C. (2,1) D. (2,-1) E. (1,2)

When reflected about line y=-x the x co-ordinate -2 becomes y co-ordinate and y cordinate 1 becomes x co-ordinate.
Since (-2,1) is in 2nd quadrant we interchange signs annd get (-1,2)

So ans: A
VP
Status: Learning
Joined: 20 Dec 2015
Posts: 1010
Location: India
Concentration: Operations, Marketing
GMAT 1: 670 Q48 V36
GRE 1: Q157 V157
GPA: 3.4
WE: Engineering (Manufacturing)
Which of the following points is reflect to y=-x at (-2,1)?  [#permalink]

Show Tags

02 Sep 2017, 23:34
ScottTargetTestPrep wrote:
MathRevolution wrote:
Which of the following points is reflect to y=-x at (-2,1)?

A. (-1, 2) B. (1,-2) C. (2,1) D. (2,-1) E. (1,2)

When reflecting a point across the line y = -x, we can follow this rule:

If coordinates (a,b) are reflected across the line y = -x, then the new reflected coordinates are (-b, -a).

Thus, when (-2,1) is reflected across the line y = -x, the new reflected coordinates are (-1,2).

Hi Sir ,

Can you give theory regarding these kinds of problems .

Regards,
Arvind
_________________
Please give kudos if you found my answers useful
Math Expert
Joined: 02 Sep 2009
Posts: 55267
Re: Which of the following points is reflect to y=-x at (-2,1)?  [#permalink]

Show Tags

03 Sep 2017, 04:34
arvind910619 wrote:
ScottTargetTestPrep wrote:
MathRevolution wrote:
Which of the following points is reflect to y=-x at (-2,1)?

A. (-1, 2) B. (1,-2) C. (2,1) D. (2,-1) E. (1,2)

When reflecting a point across the line y = -x, we can follow this rule:

If coordinates (a,b) are reflected across the line y = -x, then the new reflected coordinates are (-b, -a).

Thus, when (-2,1) is reflected across the line y = -x, the new reflected coordinates are (-1,2).

Hi Sir ,

Can you give theory regarding these kinds of problems .

Regards,
Arvind

No specific theory on this but you can check similar questions to practice:
http://gmatclub.com/forum/in-the-xy-coo ... 43502.html
http://gmatclub.com/forum/in-the-rectan ... 32646.html
http://gmatclub.com/forum/the-coordinat ... 27769.html
http://gmatclub.com/forum/the-line-repr ... 27770.html
http://gmatclub.com/forum/if-point-a-co ... 41972.html
http://gmatclub.com/forum/in-the-rectan ... 88473.html
http://gmatclub.com/forum/in-the-rectan ... 44774.html
http://gmatclub.com/forum/the-line-repr ... 87573.html
https://gmatclub.com/forum/in-the-recta ... 29932.html

Hope it helps.
_________________
Current Student
Joined: 21 Oct 2014
Posts: 53
GMAT 1: 710 Q48 V40
GMAT 2: 740 Q49 V41
GPA: 3.83
WE: Engineering (Energy and Utilities)
Re: Which of the following points is reflect to y=-x at (-2,1)?  [#permalink]

Show Tags

05 Sep 2017, 17:31
arvind910619 wrote:
ScottTargetTestPrep wrote:
MathRevolution wrote:
Which of the following points is reflect to y=-x at (-2,1)?

A. (-1, 2) B. (1,-2) C. (2,1) D. (2,-1) E. (1,2)

When reflecting a point across the line y = -x, we can follow this rule:

If coordinates (a,b) are reflected across the line y = -x, then the new reflected coordinates are (-b, -a).

Thus, when (-2,1) is reflected across the line y = -x, the new reflected coordinates are (-1,2).

Hi Sir ,

Can you give theory regarding these kinds of problems .

Regards,
Arvind

Quick Theory: Let the reflected point be (x,y). The line joining points (-2,1) and (x,y) will be perpendicular to the mirror line.

Mirror line => y = -x has slope = -1. Therefore the line joining reflected and actual points will have slope = 1.

Using the slope rise/run form for the line joining original and reflected point we get:

1 = (y - 1)/(x - (-2))

1 = (y-1)/(x+2)

y-1 = x + 2

y = x + 3

Only Option A satisfies this condition
Intern
Joined: 13 Jan 2017
Posts: 28
Re: Which of the following points is reflect to y=-x at (-2,1)?  [#permalink]

Show Tags

06 Sep 2017, 13:52
A.

Consider a circle with the centre in origin and radius-end point in (-2,1).
Graph y = -x is a diameter to this circle, so our answer comes from symmetry with respect to this diameter (y = -x).
+you may play with triangular equalities/symmetries and so on:)
SVP
Joined: 12 Dec 2016
Posts: 1530
Location: United States
GMAT 1: 700 Q49 V33
GPA: 3.64
Re: Which of the following points is reflect to y=-x at (-2,1)?  [#permalink]

Show Tags

10 Jan 2018, 03:13
Sherlock221b wrote:
Y=-x is a line in second quadrant.
And point (-2,1) lies below it so its reflection to y=-× will be opposite but in the same quadrant .
So D

Sent from my SM-G610F using GMAT Club Forum mobile app

your method is brilliant, but since gmat does not allow test takers to bring rulers, ones will find difficult to estimate the quadrant of a point given annoying locations.
Also, your method is correct, but your calculation is incorrect. OA is A.
SVP
Joined: 12 Dec 2016
Posts: 1530
Location: United States
GMAT 1: 700 Q49 V33
GPA: 3.64
Re: Which of the following points is reflect to y=-x at (-2,1)?  [#permalink]

Show Tags

10 Jan 2018, 03:29
ScottTargetTestPrep wrote:
MathRevolution wrote:
Which of the following points is reflect to y=-x at (-2,1)?

A. (-1, 2) B. (1,-2) C. (2,1) D. (2,-1) E. (1,2)

When reflecting a point across the line y = -x, we can follow this rule:

If coordinates (a,b) are reflected across the line y = -x, then the new reflected coordinates are (-b, -a).

Thus, when (-2,1) is reflected across the line y = -x, the new reflected coordinates are (-1,2).

ScottTargetTestPrep
hello, does your method apply to the general form of any linear equatation y = mx + n ?
Target Test Prep Representative
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 6207
Location: United States (CA)
Re: Which of the following points is reflect to y=-x at (-2,1)?  [#permalink]

Show Tags

12 Jan 2018, 12:38
1
chesstitans wrote:
ScottTargetTestPrep wrote:
MathRevolution wrote:
Which of the following points is reflect to y=-x at (-2,1)?

A. (-1, 2) B. (1,-2) C. (2,1) D. (2,-1) E. (1,2)

When reflecting a point across the line y = -x, we can follow this rule:

If coordinates (a,b) are reflected across the line y = -x, then the new reflected coordinates are (-b, -a).

Thus, when (-2,1) is reflected across the line y = -x, the new reflected coordinates are (-1,2).

ScottTargetTestPrep
hello, does your method apply to the general form of any linear equatation y = mx + n ?

Hi chesstitans,

No, it doesn't apply to any line in the form of y = mx + b (for any value of m and b). The formula works here for y = -x because y = -x is a special line (it makes a 45-degree angle with the negative x-axis). The same goes for lines y = x, y = 0, and x = 0 because they are special lines. However, it doesn't apply to any line in general. That said, there is a formula for reflecting a point of a line in the form of y = mx + b. However, that formula is not easy to memorize, so when a problem arises--for example, reflect (1, 2) over y = 3x + 4--we deal with it individually using concepts of coordinate geometry rather than a formula that few people can memorize.
_________________

Scott Woodbury-Stewart

Founder and CEO

Scott@TargetTestPrep.com
122 Reviews

5-star rated online GMAT quant
self study course

See why Target Test Prep is the top rated GMAT quant course on GMAT Club. Read Our Reviews

If you find one of my posts helpful, please take a moment to click on the "Kudos" button.

Re: Which of the following points is reflect to y=-x at (-2,1)?   [#permalink] 12 Jan 2018, 12:38
Display posts from previous: Sort by

Which of the following points is reflect to y=-x at (-2,1)?

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

 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®.