Results 1 to 5 of 5

Math Help - Slope of polar curve

  1. #1
    Member
    Joined
    Apr 2009
    Posts
    83

    Slope of polar curve

    Find the slope of the polar curve at the indicated point.
    r=8(1+cos theta) theta=pi/4

    I must be doing it wrong because I took the derivative of r and got:
    dr/dtheta = -8sin theta= -4 radical 2.
    The answer is 1-radical 2

    Whats my error?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Prove It's Avatar
    Joined
    Aug 2008
    Posts
    11,548
    Thanks
    1418
    Quote Originally Posted by krzyrice View Post
    Find the slope of the polar curve at the indicated point.
    r=8(1+cos theta) theta=pi/4

    I must be doing it wrong because I took the derivative of r and got:
    dr/dtheta = -8sin theta= -4 radical 2.
    The answer is 1-radical 2

    Whats my error?
    r = 8(1 + \cos{\theta})

    \frac{dr}{d\theta} = -8\sin{\theta}.


    So when \theta = \frac{\pi}{4}

    \frac{dr}{d\theta} = -8\sin{\frac{\pi}{4}}

     = -8\left(\frac{\sqrt{2}}{2}\right)

     = -4\sqrt{2}.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Apr 2009
    Posts
    83
    yes that is what i got but the answer is 1-radical 2
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor
    Prove It's Avatar
    Joined
    Aug 2008
    Posts
    11,548
    Thanks
    1418
    Quote Originally Posted by krzyrice View Post
    yes that is what i got but the answer is 1-radical 2
    Then either the answer is wrong or you copied down the question wrongly.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Member
    Joined
    Apr 2009
    Posts
    83
    weird. i didn't copy the problem wrong. it must be a coincidence because it seems the problem after that is wrong too
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 1
    Last Post: July 21st 2010, 10:57 AM
  2. slope of tangent line to polar curve
    Posted in the Calculus Forum
    Replies: 1
    Last Post: May 26th 2010, 09:00 AM
  3. Area of a Polar Curve Above the Polar Axis
    Posted in the Calculus Forum
    Replies: 6
    Last Post: May 14th 2009, 01:41 PM
  4. Replies: 1
    Last Post: January 26th 2009, 05:13 PM
  5. slope of a curve
    Posted in the Calculus Forum
    Replies: 8
    Last Post: April 10th 2008, 01:49 PM

Search Tags


/mathhelpforum @mathhelpforum