Writing an Expression...2

Discussion in 'Geometry and Trigonometry' started by nycmathguy, Nov 25, 2021.

  1. nycmathguy

    nycmathguy

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    Section 4.7

    20211120_183519.jpg

    Question 66

    sec (arctan 3x)

    Let u = arctan 3x

    This means that tan u = 3x.

    I know that tan u = opp/adj.

    Using the Pythagorean Theorem, I found the hypotenuse to be sqrt{1 - 9x^2}.

    After the u-substitution, the given problem becomes sec u.

    I know that sec u = hyp/adj.

    My answer is sec u = sqrt{1 - 9x^2}/1, which is simply sqrt{1 - 9x^2}.

    However, the correct answer according to Photomath is sqrt{1 + 9x^2}.

    Why is my answer wrong?

    This ends Section 4.7.
     
    nycmathguy, Nov 25, 2021
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  2. nycmathguy

    HallsofIvy

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    No, it's sqrt(1+ 9x^2).

     
    HallsofIvy, Nov 25, 2021
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  3. nycmathguy

    nycmathguy

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    I did try as you can see.
     
    nycmathguy, Nov 25, 2021
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