Page 1 of 2 12 LastLast
Results 1 to 15 of 21

Math Help - write the gradient of the line perpendicular to...?

  1. #1
    Super Member
    Joined
    Oct 2008
    From
    Bristol, England
    Posts
    897

    write the gradient of the line perpendicular to...?

    hi,

    i need to know how to write the gradient of the line perpendicular to Y=3x+1.

    i don't really know how to do this and some help would be great!!!

    thanks!

    p.s. sorry if topic is in wrong place, wasn't sure where to post.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,711
    Thanks
    1640
    Awards
    1

    Re: write the gradient of the line perpendicular to...?

    Quote Originally Posted by andyboy179 View Post
    i need to know how to write the gradient of the line perpendicular to Y=3x+1.
    Given the line y=mx+b,~m\ne 0 then the line y=\frac{-1}{m}x+c is perpendicular to the given line.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Super Member
    Joined
    Oct 2008
    From
    Bristol, England
    Posts
    897

    Re: write the gradient of the line perpendicular to...?

    i don't understand hot you got y=-1/mx+c. is that the gradient?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Super Member
    Joined
    Oct 2008
    From
    Bristol, England
    Posts
    897

    Re: write the gradient of the line perpendicular to...?

    the gradient of this is 3/1 =3
    so to get the perpendicular gradient would i swap them around and swap the sign on top?
    so i would have -1/3=-0.3??
    Follow Math Help Forum on Facebook and Google+

  5. #5
    MHF Contributor Siron's Avatar
    Joined
    Jul 2011
    From
    Norway
    Posts
    1,250
    Thanks
    20

    Re: write the gradient of the line perpendicular to...?

    If m is the gradient of the line y=mx+c than 1/m is the gradient of the line: y=-1/mx+C perpendicular to y=mx+c.
    And also: m\cdot \frac{-1}{m}=-1.
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Super Member
    Joined
    Oct 2008
    From
    Bristol, England
    Posts
    897

    Re: write the gradient of the line perpendicular to...?

    Okay. Can we go through this one step at a time?

    1. Is the gradient 1/3?

    2. If so is the gradient of the line perpendicular to Y=3x+1 =-3/1?

    3. Again, if so would the final answer be Y=-3/1x+1?


    If this is not correct can you point out which step of what i have said is wrong please.
    Follow Math Help Forum on Facebook and Google+

  7. #7
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,711
    Thanks
    1640
    Awards
    1

    Re: write the gradient of the line perpendicular to...?

    Quote Originally Posted by andyboy179 View Post
    write the gradient of the line perpendicular to y=3x+1.
    The gradient of the line perpendicular to y=3x+1 is ~~\frac{-1}{3}
    Follow Math Help Forum on Facebook and Google+

  8. #8
    Super Member
    Joined
    Oct 2008
    From
    Bristol, England
    Posts
    897

    Re: write the gradient of the line perpendicular to...?

    oh i thought you swap them around and swap the sign on the top one. Thanks!!

    would i just write -1/3 for the answer or would i need to put it in form of Y=mx+c?
    Follow Math Help Forum on Facebook and Google+

  9. #9
    MHF Contributor Siron's Avatar
    Joined
    Jul 2011
    From
    Norway
    Posts
    1,250
    Thanks
    20

    Re: write the gradient of the line perpendicular to...?

    It depends, if they just ask to give the gradient it satisfies to write: -1/3.
    If they ask to find the equation of the straight line with the gradient -1/3 you have to write it in the form:
    y=mx+c
    Follow Math Help Forum on Facebook and Google+

  10. #10
    Super Member
    Joined
    Oct 2008
    From
    Bristol, England
    Posts
    897

    Re: write the gradient of the line perpendicular to...?

    mine is in form of y=mx+c, so i would put y=-1/3x+1?
    Follow Math Help Forum on Facebook and Google+

  11. #11
    Super Member
    Joined
    Oct 2008
    From
    Bristol, England
    Posts
    897

    Re: write the gradient of the line perpendicular to...?

    also can the perendicular gradient denominator be a minus?
    Follow Math Help Forum on Facebook and Google+

  12. #12
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,711
    Thanks
    1640
    Awards
    1

    Re: write the gradient of the line perpendicular to...?

    Quote Originally Posted by andyboy179 View Post
    also can the perendicular gradient denominator be a minus?
    All three of these forms are the equal.
    -\frac{1}{3}=\frac{-1}{3}=\frac{1}{-3}.

    The first two are preferred.
    Follow Math Help Forum on Facebook and Google+

  13. #13
    Super Member
    Joined
    Oct 2008
    From
    Bristol, England
    Posts
    897

    Re: write the gradient of the line perpendicular to...?

    Quote Originally Posted by Plato View Post
    All three of these forms are the equal.
    -\frac{1}{3}=\frac{-1}{3}=\frac{1}{-3}.

    The first two are preferred.
    ok thank, i was just curious, however back to my question would the final answer be y=-1/3x+1?
    Follow Math Help Forum on Facebook and Google+

  14. #14
    MHF Contributor Siron's Avatar
    Joined
    Jul 2011
    From
    Norway
    Posts
    1,250
    Thanks
    20

    Re: write the gradient of the line perpendicular to...?

    You have the equation of the (given) line:
    y=3x+1
    And now you've found the gradient of a line perpendicular to y as you know.
    In y the 1 is the point at which the line y crosses the y-axis, this hasn't to be the same for the line perpendicular to y, you've a lot of options. You only have the choose one.
    (You only have one option when they ask to give the equation of the line perpendicular to y and going through a given point)

    So maybe it's a little bit confusing but draw y=3x+1, now draw a line perpendicular to y and look where that line crosses the y-axis so you can create the equation of the line perpendicular to y.

    Is that clear or? ...
    Follow Math Help Forum on Facebook and Google+

  15. #15
    Super Member
    Joined
    Oct 2008
    From
    Bristol, England
    Posts
    897

    Re: write the gradient of the line perpendicular to...?

    mine crossed the y axis at 1? is that okay
    Follow Math Help Forum on Facebook and Google+

Page 1 of 2 12 LastLast

Similar Math Help Forum Discussions

  1. Perpendicular line.
    Posted in the Algebra Forum
    Replies: 1
    Last Post: October 4th 2011, 06:26 PM
  2. Replies: 4
    Last Post: May 12th 2011, 12:18 PM
  3. perpendicular gradient proof
    Posted in the Geometry Forum
    Replies: 5
    Last Post: July 29th 2010, 01:21 AM
  4. Finding a line perpendicular to another line
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: December 12th 2009, 09:13 PM
  5. equation of a line perpendicular to the line defined
    Posted in the Pre-Calculus Forum
    Replies: 2
    Last Post: June 6th 2007, 09:02 AM

Search Tags


/mathhelpforum @mathhelpforum