In the xy coordinate system, if (a,b) and (a+3, b+k) are two points on the line defined by the equation x=3y-7, then k =
A. 9
B. 3
C. 7/3
D. 1
E. 1/3
Answer is D
How do I approach this problem? Also, could someone tell me how to tell if two lines are parallel?
Thanks so much!
xy coordinate system??
This topic has expert replies
GMAT/MBA Expert
- Anurag@Gurome
- GMAT Instructor
- Posts: 3835
- Joined: Fri Apr 02, 2010 10:00 pm
- Location: Milpitas, CA
- Thanked: 1854 times
- Followed by:523 members
- GMAT Score:770
The equation of the line is given by: y = mx + bgmatpup wrote:In the xy coordinate system, if (a,b) and (a+3, b+k) are two points on the line defined by the equation x=3y-7, then k =
A. 9
B. 3
C. 7/3
D. 1
E. 1/3
Answer is D
How do I approach this problem? Also, could someone tell me how to tell if two lines are parallel?
Thanks so much!
Now put x = 3y - 7 in the above form, y = (1/3)x + 7/3.
m = 1/3
Since (a, b) and (a+3, b+k) are two points on the line, and slope of a line passing through two points (x1, y1) and (x2, y2) = (y2 - y1)/(x2 - x1)
[(b + k) - b]/[(a + 3) - a] = 1/3
k/3 = 1/3
k = 1
The correct answer is D.
Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)
Join Our Facebook Groups
GMAT with Gurome
https://www.facebook.com/groups/272466352793633/
Admissions with Gurome
https://www.facebook.com/groups/461459690536574/
Career Advising with Gurome
https://www.facebook.com/groups/360435787349781/
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)
Join Our Facebook Groups
GMAT with Gurome
https://www.facebook.com/groups/272466352793633/
Admissions with Gurome
https://www.facebook.com/groups/461459690536574/
Career Advising with Gurome
https://www.facebook.com/groups/360435787349781/
- neelgandham
- Community Manager
- Posts: 1060
- Joined: Fri May 13, 2011 6:46 am
- Location: Utrecht, The Netherlands
- Thanked: 318 times
- Followed by:52 members
Method 1: Using the slope formula! The equation of any line can be represented in the form y = mx + c where m is the slope and c is the y interceptgmatpup wrote:In the xy coordinate system, if (a,b) and (a+3, b+k) are two points on the line defined by the equation x=3y-7, then k =
A. 9
B. 3
C. 7/3
D. 1
E. 1/3
How do I approach this problem?
x=3y-7 => y = (x+7)/3 = (1/3)*x + (7/3) = mx + c. So the slope of the line m = 1/3
To find the slope, you can also use the following formula:
Slope m = (y2-y1)/(x2-x1) where (x1,y1) and (x2,y2) are points that lie on the line y = mx + c
Slope m = (b+k-k)/(a+3-a) = k/3 = 1/3 => k = 1
Method 2: Substitution
We know x=3y-7 and points (a,b),(a+3,b+k) lie on the line.
So, substituting the values of (a,b)and (a+3,b+k) in the equation x=3y-7 we get
a = 3b - 7 => a -3b = -7 - (1)
a + 3 = 3b + 3k -7 => a = 3b -3 + 3k -7 => a -3b = -3 + 3k -7 - (2)
Equating the terms of right hand side of equations (1) and (2), you get
-7 = -3 + 3k -7 => 3k = 3 => k = 1
IMO D
Since slope is a measure of the angle of a line from the horizontal, and since parallel lines must have the same angle, the parallel lines have the same slope - and lines with the same slope are parallel.Also, could someone tell me how to tell if two lines are parallel?
If lines y = mx + c and y = nx + d are parallel then the value of m and n should be equal
Anil Gandham
Welcome to BEATtheGMAT | Photography | Getting Started | BTG Community rules | MBA Watch
Check out GMAT Prep Now's online course at https://www.gmatprepnow.com/
Welcome to BEATtheGMAT | Photography | Getting Started | BTG Community rules | MBA Watch
Check out GMAT Prep Now's online course at https://www.gmatprepnow.com/
Doesn't this mean that the two lines are part of x=3y-7?
I just solved for y and then plugged in numbers.
Since we know y= x/3 + 7/3
I made x = 2 and then solved for the problem if x was +3, which resulted in y making a change from 3 to 4 equal to 1, the change of y.
I just solved for y and then plugged in numbers.
Since we know y= x/3 + 7/3
I made x = 2 and then solved for the problem if x was +3, which resulted in y making a change from 3 to 4 equal to 1, the change of y.
GMAT/MBA Expert
- Brent@GMATPrepNow
- GMAT Instructor
- Posts: 16207
- Joined: Mon Dec 08, 2008 6:26 pm
- Location: Vancouver, BC
- Thanked: 5254 times
- Followed by:1268 members
- GMAT Score:770
Key Concept: If a point lies ON a line, then the coordinates (x and y) of that point must SATISFY the equation of that line.
Given equation: x = 3y - 7
One point ON the line is (a, b)
So, we can write: a = 3b - 7
Another point ON the line is (a + 3, b + k)
So, we can write: a + 3 = 3(b + k) - 7
Expand: a + 3 = 3b + 3k - 7
Subtract 3 from both sides to get: a = 3b + 3k - 10
We now two equations:
a = 3b + 3k - 10
a = 3b - 7
Subtract the bottom equation from the top equation to get: 0 = 3k - 3
Add 3 to both sides: 3 = 3k
Solve: k = 1
Answer: D
Cheers,
Brent