Results 1 to 12 of 12

Math Help - Finding the equation of a line from two given points.

  1. #1
    Junior Member
    Joined
    May 2010
    Posts
    26

    Finding the equation of a line from two given points.

    plz neeed help with this If a line passes through the points (-2, -4) and (3, -1), the equation of the line is y + 4 = 3/5(x + _____).
    Last edited by mr fantastic; May 6th 2010 at 06:23 PM. Reason: Re-titled.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Member mohammadfawaz's Avatar
    Joined
    Feb 2010
    From
    Lebanon - Beirut
    Posts
    100
    First find the equation of the line as y=mx+b. You know how do this right?
    Now, y+4=mx+b+4 from which you should be able to factor \frac{3}{5}.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    May 2010
    Posts
    26
    i dont know how to do this so 3/5 is the answer
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor undefined's Avatar
    Joined
    Mar 2010
    From
    Chicago
    Posts
    2,340
    Awards
    1
    Quote Originally Posted by daniel323 View Post
    i dont know how to do this so 3/5 is the answer
    This question is supposed to be testing your understanding of and ability to recognize the point-slope equation.

    Do you see it?
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Junior Member
    Joined
    May 2010
    Posts
    26
    can u help with this problem also Yfrog Image : yfrog.com/j9math14p
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Member mohammadfawaz's Avatar
    Joined
    Feb 2010
    From
    Lebanon - Beirut
    Posts
    100
    Ok, first, the equation of the line should be of the form y=mx+b where m is slope and given by m=\frac{y_2-y_1}{x_2-x_1} = \frac{-1-(-4)}{3-(-2)} = \frac{3}{5}.
    Hence, y=\frac{3}{5}x+b. Still need to find b.
    the point (-2,-4) belongs to the lines, hence: -4=\frac{3}{5}\times (-2)+b, therefore: b = -4+\frac{6}{4} = -4+\frac{3}{2}.
    Hence, y=\frac{3}{5}x-4+\frac{3}{2}.
    So, y+4=\frac{3}{5}x+\frac{3}{2} = \frac{3}{5}(x+\frac{3/2}{3/5}) = \frac{3}{5}(x+\frac{5}{2}) .
    \frac{5}{2} is the answer you need.
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Junior Member
    Joined
    May 2010
    Posts
    26
    i got the first problem already but need second problem
    Follow Math Help Forum on Facebook and Google+

  8. #8
    Member mohammadfawaz's Avatar
    Joined
    Feb 2010
    From
    Lebanon - Beirut
    Posts
    100
    For the second question, it is clear from the figure that the two lines are parallel. This means that they have the same slope, hence your answer is -\frac{4}{3}.
    Follow Math Help Forum on Facebook and Google+

  9. #9
    Junior Member
    Joined
    May 2010
    Posts
    26
    thank u so much.
    Last edited by mr fantastic; May 6th 2010 at 06:16 PM.
    Follow Math Help Forum on Facebook and Google+

  10. #10
    A riddle wrapped in an enigma
    masters's Avatar
    Joined
    Jan 2008
    From
    Big Stone Gap, Virginia
    Posts
    2,551
    Thanks
    12
    Awards
    1
    Quote Originally Posted by daniel323 View Post
    plz neeed help with this If a line passes through the points (-2, -4) and (3, -1), the equation of the line is y + 4 = 3/5(x + _____).
    Hi daniel323,

    Are you familiar with the 'point-slope' form of a linear equation:

    y-y_1=m(x-x_1)

    Find your slope, which is already given to you as \frac{3}{5}

    Use (-2, -4) as (x_1, y_1) and the equation:

    y-y_1=m(x-x_1)

    And fill in the blank:  y-(-4)=\frac{3}{5}(x-(-2))\Longrightarrow \boxed{y+4=\frac{3}{5}(x+{\color{red}2})}

    2 is the answer you need.
    Follow Math Help Forum on Facebook and Google+

  11. #11
    MHF Contributor undefined's Avatar
    Joined
    Mar 2010
    From
    Chicago
    Posts
    2,340
    Awards
    1
    Quote Originally Posted by mohammadfawaz View Post
    Ok, first, the equation of the line should be of the form y=mx+b where m is slope and given by m=\frac{y_2-y_1}{x_2-x_1} = \frac{-1-(-4)}{3-(-2)} = \frac{3}{5}.
    Hence, y=\frac{3}{5}x+b. Still need to find b.
    the point (-2,-4) belongs to the lines, hence: -4=\frac{3}{5}\times (-2)+b, therefore: b = -4+\frac{6}{4} = -4+\frac{3}{2}.
    Hence, y=\frac{3}{5}x-4+\frac{3}{2}.
    So, y+4=\frac{3}{5}x+\frac{3}{2} = \frac{3}{5}(x+\frac{3/2}{3/5}) = \frac{3}{5}(x+\frac{5}{2}) .
    \frac{5}{2} is the answer you need.
    I know the OP said this problem is already solved, but I'd just like to point out that there is an error here, there was a (6/4) where there should have been a (6/5), and the value for b is wrong.

    Using point-slope equation, once you verify that the slope is (3/5), you can immediately see that the answer is 2.

    Edit: Ah, masters beat me to it.
    Follow Math Help Forum on Facebook and Google+

  12. #12
    Member mohammadfawaz's Avatar
    Joined
    Feb 2010
    From
    Lebanon - Beirut
    Posts
    100
    Oh!
    sorry for that!
    I had a typing mistake that got me all wrong,
    So, 2 is the correct answer
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. FInding Points of Tangent Line w/ Vectors
    Posted in the Calculus Forum
    Replies: 3
    Last Post: November 10th 2010, 11:58 AM
  2. Finding equation of a line given two points.
    Posted in the Algebra Forum
    Replies: 3
    Last Post: May 6th 2010, 06:24 PM
  3. Replies: 3
    Last Post: March 17th 2010, 04:54 AM
  4. Replies: 1
    Last Post: November 5th 2009, 01:32 PM
  5. Points on a graph (tangent line finding)
    Posted in the Pre-Calculus Forum
    Replies: 4
    Last Post: May 31st 2009, 08:16 AM

Search Tags


/mathhelpforum @mathhelpforum