Author 
Message 
TAGS:

Hide Tags

Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 5452
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
This post received KUDOS
Expert's post
5
This post was BOOKMARKED
Question Stats:
54% (00:51) correct 46% (00:44) wrong based on 155 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)
Official Answer and Stats are available only to registered users. Register/ Login.
_________________
MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The oneandonly World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only $79 for 3 month Online Course" "Free Resources30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons  try it yourself"



Intern
Joined: 04 Jan 2017
Posts: 7

Re: Which of the following points is reflect to y=x at (2,1)? [#permalink]
Show Tags
06 Jan 2017, 09:20
1
This post received KUDOS
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 SMG610F using GMAT Club Forum mobile app



Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 5452
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
This post received KUDOS
Expert's post
2
This post was BOOKMARKED
==> You can figure out a point reflecting to y=x by substituting –y to xcoordinate and –x to ycoordinate. Then, (2,1) > (1, (2))=(1,2) is derived. Hence, the answer is A. Answer: A
_________________
MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The oneandonly World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only $79 for 3 month Online Course" "Free Resources30 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: 2638
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
This post received KUDOS
Expert's post
2
This post was BOOKMARKED
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). Answer: A
_________________
Scott WoodburyStewart
Founder and CEO
GMAT Quant SelfStudy Course
500+ lessons 3000+ practice problems 800+ HD solutions



Director
Joined: 12 Nov 2016
Posts: 776
Location: United States
GRE 1: 315 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 coordinate 2 becomes y coordinate and y cordinate 1 becomes x coordinate. 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: 1147
Location: India
Concentration: Operations, Marketing
GRE 1: 314 Q157 V157
GPA: 3.4
WE: Manufacturing and Production (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). Answer: A 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: 45497

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). Answer: A 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/inthexycoo ... 43502.htmlhttp://gmatclub.com/forum/intherectan ... 32646.htmlhttp://gmatclub.com/forum/thecoordinat ... 27769.htmlhttp://gmatclub.com/forum/thelinerepr ... 27770.htmlhttp://gmatclub.com/forum/ifpointaco ... 41972.htmlhttp://gmatclub.com/forum/intherectan ... 88473.htmlhttp://gmatclub.com/forum/intherectan ... 44774.htmlhttp://gmatclub.com/forum/thelinerepr ... 87573.htmlhttps://gmatclub.com/forum/intherecta ... 29932.htmlHope it helps.
_________________
New to the Math Forum? Please read this: Ultimate GMAT Quantitative Megathread  All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



Manager
Joined: 21 Oct 2014
Posts: 53
Location: Canada
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). Answer: A 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 = (y1)/(x+2) y1 = x + 2 y = x + 3 Only Option A satisfies this condition



Intern
Joined: 13 Jan 2017
Posts: 29

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 radiusend 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: 1905
Location: United States
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 SMG610F using GMAT Club Forum mobile appyour 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: 1905
Location: United States
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). Answer: A ScottTargetTestPrephello, 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: 2638
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
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). Answer: A ScottTargetTestPrephello, 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 45degree angle with the negative xaxis). 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 arisesfor example, reflect (1, 2) over y = 3x + 4we deal with it individually using concepts of coordinate geometry rather than a formula that few people can memorize.
_________________
Scott WoodburyStewart
Founder and CEO
GMAT Quant SelfStudy Course
500+ lessons 3000+ practice problems 800+ HD solutions




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






