1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Finding slope of tangetns

  1. Apr 14, 2008 #1
    Find the slope of the tangent to the parabola y=-3x^2 + 4x - 7 when x=a. I know how to get the limit using the tangent so i end up with a slope in terms of a (you can also get it using the derivative) but now the next part states:
    At what point on the parabola is the tangent perpendicular to the line 3x - 4y + 8=0 and all that i get from that question is that the tangent for the point on the parabola will have a slope of -4/3 (negative reciprocal)
    Last edited: Apr 14, 2008
  2. jcsd
  3. Apr 14, 2008 #2
    so you have the derivative in terms of a, right? Let's call it D(a).

    You're looking for the value for a such that this expression is equal to -4/3.

    So what about solving D(a)=-4/3 for a ..?
  4. Apr 14, 2008 #3
    sorry... so if the derivative is 6x + 4, then i can say that 6x + 4= -4/3 and solve for a (or x)?
  5. Apr 14, 2008 #4
    Exactly, sometimes it's easier than you think :smile:
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Finding slope of tangetns