Results 1 to 5 of 5

Math Help - find equation of line

  1. #1
    Newbie
    Joined
    Feb 2008
    Posts
    20

    find equation of line

    Cant solve this problem. Have and exam coming very soon.

    Write down the equation of any line through the point (-4, 2)
    Hence find the equations of the two lines through the point (-4, 2) whose perpendicular distance from the origin is 2.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Senior Member
    Joined
    Mar 2008
    From
    Pennsylvania, USA
    Posts
    269
    Thanks
    37
    This is for a geometry class?? Sounds more like Algebra 2 or maybe the beginning of a pre-calc/college algebra course. Nonetheless, follow below:

    You want the equation of any line that goes through (-4, 2).

    Let's make it simple: set up y = mx + b and we can even for your own convenience let m be 1. Thus, y = x + b is appropriate. Lets plug in -4 as our x-coord and 2 as our y-cord. We now have: 2 = -4 + b

    In this case, (and there are infinitely many), 2 = -4 + 6, so:

    y = x + 6 is an equation that goes through (-4, 2).

    -Andy
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Feb 2008
    Posts
    20
    Thanks but you did not answer the second part of the question. In know the first part.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Junior Member
    Joined
    Mar 2008
    Posts
    43
    i get one line within 1 second.....
    y=2
    lol....
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Junior Member
    Joined
    Mar 2008
    Posts
    43
    the other one i get is y=-4/3x-10/3
    i list a three unknown equation
    the line pass through -4,2 _so 2=-4m+b let b write as m_ b = 2+4m
    the first equation is y=mx+2+4m
    the question said the distance from the origin to the line is 2, so let's draw a line through the origin that can be perpendicular the line
    -any line pass through the origin can be write as y=mx
    -if two lines are perpendicular to each other, their slopes have a productof -1
    so the second equation is y=-1/mx(-1/m compare to the line we need to calculate)
    third the the vertical distance from the origin to the line is 2
    so we can write it as x^2+y^2=2^2
    now we have three equations with three unknows
    y=mx+2+4m
    y=-1/mx
    x^2+y^2=2^2
    then solve for the equation. i get x= -8/5 and y= -6/5
    then solve the equation pass through 2 points (-4,2),(-8/5, -6/5)
    i don't know if i get the right equation, but i'm pretty sure i use the right method....
    i hope this helps, can somebody confirm my answer , thank you
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 8
    Last Post: March 22nd 2011, 04:57 PM
  2. Replies: 1
    Last Post: March 18th 2011, 10:36 AM
  3. Replies: 9
    Last Post: July 31st 2009, 05:39 AM
  4. Replies: 11
    Last Post: June 2nd 2009, 06:08 PM
  5. Replies: 5
    Last Post: October 13th 2008, 10:16 AM

Search Tags


/mathhelpforum @mathhelpforum