Results 1 to 2 of 2

Math Help - Find the equation of the line?

  1. #1
    Member
    Joined
    Jan 2009
    Posts
    197

    Exclamation Find the equation of the line?

    Question:
    FInd the equation of the normal lines to the curve  y=x^3-3x which is parallel to the line of  2x+18y-9=0

    Attempt:
     f'(x)=3x^2-3
     m=9
     x=2 ;y=2
     y-2=9(x-2)

    Is my equation correct?
    If not please answer in steps
    Thank you
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Sep 2008
    From
    West Malaysia
    Posts
    1,261
    Quote Originally Posted by mj.alawami View Post
    Question:
    FInd the equation of the normal lines to the curve  y=x^3-3x which is parallel to the line of  2x+18y-9=0

    Attempt:
     f'(x)=3x^2-3
     m=9
     x=2 ;y=2
     y-2=9(x-2)

    Is my equation correct?
    If not please answer in steps
    Thank you
    HI


    y=x^3-3x\Rightarrow \frac{dy}{dx}=3x^2-3

    This is the gradient of tangent . The gradient of normal would be perpendicular to it .

    Gradient of normal , call it M2 is -\frac{1}{9} (do u know y)

    (3x^2-3)(M2)=-1

    -\frac{1}{9}=-\frac{1}{3x^2-3}

    solving this ... x=\pm 2

    Put this into the original equation (curve) to find the y's .
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 8
    Last Post: March 22nd 2011, 05:57 PM
  2. Replies: 1
    Last Post: March 18th 2011, 11:36 AM
  3. Replies: 9
    Last Post: July 31st 2009, 06:39 AM
  4. Replies: 11
    Last Post: June 2nd 2009, 07:08 PM
  5. Replies: 5
    Last Post: October 13th 2008, 11:16 AM

Search Tags


/mathhelpforum @mathhelpforum