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.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 500,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

Does line Ax + By + C = 0 (A is not 0) intersect the x-axis on the negative side?

1. BA <0> 0

Please explain your answer.

Getting E.

Ax + By + C = 0
By = -Ax - C (cannot divide by B just yet since B could be 0)

Stat 1:
Tells us that B is not 0 and that A and B have the same sign.
y = - (A/B)x - C
To find x, y = 0:
-(A/B)x = C
x = -(B/A) * C
B/A will have the same sign therefore -(B/A) will be negative which makes me think that the answer to the stem is yes. However, what if C = 0? The answer to the stem is no. Insuff.

Stat 2:
Tells us that A & C have opposite signs. I don't think that this alone helps us in determine the answer. Insuff.

Together:
If A is +ve and C is -ve then x intercept is +ve
If A is -ve and C is +ve then x intercept is -ve
Insuff.

Re: Does line Ax + By + C = 0 (A is not 0) intersect the x-axis [#permalink]

Show Tags

12 Nov 2013, 22:23

@laserglare

Yes, to find the x-intercept of a line, the point where it intersects the x-axis, we set the y-coordinate to 0. You correctly replaced y as 0 in the equation Ax+By+C=0, which gave you the x-intercept of -C/A.

Here 2 alone is sufficient because if AC>0, then we have either both A and C are positive or both A and C are negative, in both scenarios -C/A is negative, meaning the x-intercept is negative or intersects the x-axis to the left of the origin.

i was doing this on the gmatclub tests and i cannot figure out why all we need is x = -c/a

"So, the x-intercept of line ax+by+c=0 is x=−c/a." I plugged in 0 so ax+ by+ c = 0 then y = ( -ax - c ) / b

was i supposed to think of this question like this ax + b (0) + c = 0 ax + c = 0 x = -c/a

then use that equation to figure out what x is???

(when i was doing this before viewing the solution, i assumed that we would need a/b to solve because -a/b * x.)

Given Ax + By + C = 0 is the equation of a line. You need to figure out whether it intersects x axis on the negative side i.e. in the second quadrant. You want to know that when the line crosses the x axis (if it does), is x co-ordinate negative there? When does a line cross the x axis? When its y co-ordinate is 0. So how will you know the point where the line crosses the x axis? You put y = 0. Ax + B*0 + C = 0 x = -C/A So when y = 0, x = -C/A

We want to know whether this x cor-ordinate (-C/A) is negative. It will be negative when C/A is positive i.e. both C and A will have the same sign (either both positive or both negative) Statement 2 tells you that C and A have the same sign (since their product is positive). Hence it is enough alone.

Does line Ax + By + C = 0 (A is not 0) intersect the x-axis on the negative side?

(1) BA < 0. (2) AC > 0.

M18-13

Does line Ax + By + C = 0 (A is not 0) intersect the x-axis on the negative side?

\(ax+by+c=0\) is equation of a line. Note that the line won't have interception with x-axis when \(a=0\) (and \(c\neq{0}\)): in this case the line will be \(y=-\frac{c}{b}\) and will be parallel to x -axis.

Now, in other cases (when \(a\neq{0}\)) x-intercept of a line will be the value of \(x\) when \(y=0\), so the value of \(x=-\frac{c}{a}\). Question basically asks whether this value is negative, so question asks is \(-\frac{c}{a}<0\)? --> is \(\frac{c}{a}>0\)? --> do \(c\) and \(a\) have the same sign?

(1) BA < 0. Not sufficient as we can not answer whether \(c\) and \(a\) have the same sign. (2) AC > 0 --> \(c\) and \(a\) have the same sign. Sufficient.

Re: Does line Ax + By + C = 0 (A is not 0) intersect the x-axis [#permalink]

Show Tags

03 Feb 2015, 16:08

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________

Does line Ax + By + C = 0 (A is not 0) intersect the x-axis [#permalink]

Show Tags

25 Nov 2015, 08:14

Is the x intercept of the line negative? From the given equation: x = -by/a - c/a. At x intercept of this line: y = 0 and x = - c/a.

Question reformulated: Is - c/a a negative value?

Statement 1: gives no information about c, therefore the sign of - c/a cannot be determined.

Statement 2: ac > 0. Therefore a and c have the same sign, and either both are negative or both are positive. In either case c/a becomes a positive value and - c/a is becomes a negative value, therefore the x intercept of the line is a negative value.

Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.

Does line Ax + By + C = 0 (A is not 0) intersect the x-axis on the negative side?

(1) BA < 0. (2) AC > 0.

We want to know whether in Ax+C=0, Ax=-C, x=-C/A, -C/A<0. If we multiply -A^2 on both sides, we are multiplying negative number, so the inequality sign flips. So -C/A<0? --> CA>0? Condition 2 answers this 'yes' and the answer becomes (B).

Once we modify the original condition and the question according to the variable approach method 1, we can solve approximately 30% of DS questions.
_________________

Its been long time coming. I have always been passionate about poetry. It’s my way of expressing my feelings and emotions. And i feel a person can convey...

Written by Scottish historian Niall Ferguson , the book is subtitled “A Financial History of the World”. There is also a long documentary of the same name that the...

Post-MBA I became very intrigued by how senior leaders navigated their career progression. It was also at this time that I realized I learned nothing about this during my...