Results 1 to 10 of 10

Math Help - Slope of a secant line

  1. #1
    Junior Member
    Joined
    May 2010
    Posts
    25

    Slope of a secant line

    Hey guys im having problems with this question

    Consider the graph of the function f(x)=-5x^2+3x. Determine the slope of the secant line passing though the two points of the graph when x=1 and x=3. Determine the equation of the line passing through the two points.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Mar 2010
    From
    Florida
    Posts
    3,093
    Thanks
    5
    When x=1 and x=3, y=-2 and y=-36, respectively. How do you find a slope when given two points that form a line?
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    May 2010
    Posts
    25
    You would use point slope form y-y1=m(x-x1) so can i just plug x=1 into the problem -5(1)^2+3x to get the solution?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor
    Joined
    Mar 2010
    From
    Florida
    Posts
    3,093
    Thanks
    5
    Quote Originally Posted by oregon88 View Post
    You would use point slope form y-y1=m(x-x1) so can i just plug x=1 into the problem -5(1)^2+3x to get the solution?
    That is how you get the equation for the line. Did you ever get the value of m?
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Junior Member
    Joined
    May 2010
    Posts
    25
    I was working on it, to find the slope wouldnt you start with finding the
    f '(x) (which from what I understand gives you the slope of the secant line and the slope of the tangent line)?
    Follow Math Help Forum on Facebook and Google+

  6. #6
    MHF Contributor
    Joined
    Mar 2010
    From
    Florida
    Posts
    3,093
    Thanks
    5
    Quote Originally Posted by oregon88 View Post
    I was working on it, to find the slope wouldnt you start with finding the
    f '(x) (which from what I understand gives you the slope of the secant line and the of the tangent line)?
    Slope equals rise over run. m=\frac{y_2-y_1}{x_2-x_1}

    You have two points on your secant line so why derive?
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Junior Member
    Joined
    May 2010
    Posts
    25
    Ok so how do you find the slope of the secant line at those points x=1 and x=3 i guess is where im stuck. I understand at x=1 y=0 and at x=3 y=0.
    Follow Math Help Forum on Facebook and Google+

  8. #8
    MHF Contributor
    Joined
    Mar 2010
    From
    Florida
    Posts
    3,093
    Thanks
    5
    Quote Originally Posted by oregon88 View Post
    ok so how do you find the slope of the secant line at those points x=1 and x=3 i guess is where im stuck. I understand at x=1 y=0 and at x=3 y=0. what????
    -5(1)^2+3(1)=-2

    -5(3)^2+3(3)=-45+9=-36
    Follow Math Help Forum on Facebook and Google+

  9. #9
    Junior Member
    Joined
    May 2010
    Posts
    25
    Oh so im making it harder than it really needs to be. So those are the slopes at those points. My last question is what does he mean by Determine the equation of the line passing through the two points.
    Follow Math Help Forum on Facebook and Google+

  10. #10
    MHF Contributor
    Joined
    Mar 2010
    From
    Florida
    Posts
    3,093
    Thanks
    5
    Quote Originally Posted by oregon88 View Post
    Oh so im making it harder than it really needs to be. So those are the slopes at those points. My last question is what does he mean by Determine the equation of the line passing through the two points.
    Those are the y coordinates.

    (1,-2) and (3,-36)

    m=\frac{-36-(-2)}{3-1}=\frac{-34}{2}=-17

    Find the equation of the line, use point-slope form.

    y-y_1=m(x-x_1)\rightarrow y-(-2)=(-17)(x-1)\rightarrow y=-17x+15
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Slope of a secant line
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: May 11th 2010, 04:43 AM
  2. Secant Line Slope and Tangent Line Slope
    Posted in the Calculus Forum
    Replies: 3
    Last Post: August 26th 2009, 05:40 PM
  3. slope of secant line
    Posted in the Calculus Forum
    Replies: 1
    Last Post: September 26th 2007, 05:57 PM
  4. slope of the secant line
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: February 8th 2007, 12:47 PM
  5. Slope of Secant Line
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: January 19th 2007, 06:38 PM

Search Tags


/mathhelpforum @mathhelpforum