Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Lines tangent to f(x)

  1. Sep 21, 2008 #1
    1. The problem statement, all variables and given/known data

    f(x) = 4x-x2

    Question: Find the equations of the lines that pass through P(2,7) and are tangent to the graph of f(x).

    (P is not on f(x).)
    Thats all the problem states.

    2. Relevant equations

    f(x) = 4x-x2
    Point (2,7)

    3. The attempt at a solution

    Ive tried finding f'(x) and plugging f' into the Line equation y=mx+b.


    Then plugging in Point P.

    7=(4-2x)2+b - Im not really sure if this is heading in the right direction.
  2. jcsd
  3. Sep 21, 2008 #2


    User Avatar
    Homework Helper

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook