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.

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:

Re: What is the equation of a line perpendicular to lines [#permalink]
12 Nov 2012, 01:40

seriousmonkey wrote:

It is not very difficult. Just note that slope of the line is how inclined it is with respect to the x axis.

For instance, if we have 2 coordinates: (x1,y1) and (x2,y2), we can calculate the slope(gradient) as follows:

(y2-y1)/(x2-x1)

Slope of a line is denoted by m. You can look at the line equation:

y= mx+c.

Here m is the slope and c is the y intercept or where the line cuts the y axis. In your example, just substitute x=0 in the equation and solve for y.

I do not want to go into details, but the product of the slopes of two perpendicular lines must equal -1.

So for your equation: y=2x+5

slope of this line is 2. Therefore any perpendicular line will have the slope as -1/2 since the product of 2 and -1/2 is -1.

Therefore the perpendicular will take the form: y= (-1/2)x +k, where k is the y intercept of the perpendicular line...

My doubt is really a basic one

I also solved till slope but know the y intercept can have two different values as you see we have two different equations... so we can have two different equations for the same line.... Is it possible?

Re: What is the equation of a line perpendicular to lines [#permalink]
12 Nov 2012, 03:35

No, you can't have two equations for the same line (unless you multiply by different non-zero constants on both sides- but it boils down to the same thing really)

the two equations you gave are parallel lines: they have the same slope but they cut the y axis and x axis at different points.

Re: What is the equation of a line perpendicular to lines [#permalink]
12 Nov 2012, 19:18

Firstly, there can be an infinite number of perpendicular lines to the two equations you posted. You will need some other condition to pin-point the line you need to get the answer( such as "the perpendicular line passes through a point" or something). So that is why I posted y= -1/2*x +k, because we can have any value of k and it will be perpendicular to the straight lines you posted (try plotting the lines and draw perpendicular lines- you will find you can draw many)

Re: What is the equation of a line perpendicular to lines [#permalink]
21 Nov 2012, 21:56

seriousmonkey wrote:

Firstly, there can be an infinite number of perpendicular lines to the two equations you posted. You will need some other condition to pin-point the line you need to get the answer( such as "the perpendicular line passes through a point" or something). So that is why I posted y= -1/2*x +k, because we can have any value of k and it will be perpendicular to the straight lines you posted (try plotting the lines and draw perpendicular lines- you will find you can draw many)

Hey thanks dude.. I was looking for similar thing..

I have another doubt... ways to find a equation of perpendicular line y=mx+k... such as: 1) one point and one equation of line (y=2x-5) or 2) one point and one slope of another line (m=2)

Is there any way to find this equation of perpendicular line? _________________

GMAT - Practice, Patience, Persistence Kudos if u like

Re: What is the equation of a line perpendicular to lines [#permalink]
22 Nov 2012, 03:26

Expert's post

shanmugamgsn wrote:

seriousmonkey wrote:

Firstly, there can be an infinite number of perpendicular lines to the two equations you posted. You will need some other condition to pin-point the line you need to get the answer( such as "the perpendicular line passes through a point" or something). So that is why I posted y= -1/2*x +k, because we can have any value of k and it will be perpendicular to the straight lines you posted (try plotting the lines and draw perpendicular lines- you will find you can draw many)

Hey thanks dude.. I was looking for similar thing..

I have another doubt... ways to find a equation of perpendicular line y=mx+k... such as: 1) one point and one equation of line (y=2x-5) or 2) one point and one slope of another line (m=2)

Is there any way to find this equation of perpendicular line?