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Homework Help: Linear approximation

  1. Apr 18, 2010 #1
    1. The problem statement, all variables and given/known data

    Given f(x)=sqrt(2x+2)

    Question : Find the linear approximation of f(x) at a=7 AND use it to approximate sqrt(18).


    2. Relevant equations

    L(x)=f(a)+f'(a)(x-a)

    3. The attempt at a solution

    Using the linear approximation formula I am getting the value 6.75, but when I checked with calculator the value of sqrt(18) is 4.2426....

    Did my approximation is wrong?
     
  2. jcsd
  3. Apr 18, 2010 #2

    D H

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    Staff Emeritus
    Science Advisor

    Yes, you did something wrong. Show us your work. It's kinda hard to tell where you went wrong without that.
     
  4. Apr 18, 2010 #3
    Thank you :smile:

    I didn't solve 2x+2=18. I plugged in x=18 and (x-a) becomes (18-7) = 11.

    Now I got it. Thanks.
     
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