Results 1 to 3 of 3

Math Help - Quick question about sum and difference formula

  1. #1
    Member
    Joined
    Apr 2009
    Posts
    83

    Exclamation Quick question about sum and difference formula



    I just need help on #3.

    To find the Φ of the equation wouldn't we do tan Φ = a2/a1? If so how come the answer in the back of the book says sqr2 sin(t +3pi/4).

    When I did the tan Φ = a2/a1 = -1/1 I would get a Φ angle of -0.78539.

    Please confirm if I did something wrong or the book is wrong. Thank you!
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member
    Joined
    Jun 2009
    Posts
    806
    Thanks
    4
    The given problem can be written as
    sqrt(2)[sint*-sqrt(1/2) + cos(t)*sqrt(1/2)]....(1)
    Now sin(3π/4) = sqrt(1/2)
    and cos(3π/4) = -sqrt(1/2)
    Substitute these values in eq.(1) and see what you get.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor
    Joined
    Aug 2007
    From
    USA
    Posts
    3,111
    Thanks
    2
    1) Why are you using your calculator when an exact value is requested?

    2) I'm not really sure how to help you except to provide examples of how to proceed. Usually, just try somehthing that seems to make sense and revise as necessary. Example below:

    For #3, I tried \sin\left(t - \frac{\pi}{4}\right) - Nope, not quite right. Sign is wrong.


    Then, I tried \sin\left(t - \frac{5\pi}{4}\right) - Nope, not quite right. Amplitude is wrong.


    Finally, I tried \sqrt{2}\cdot\sin\left(t - \frac{5\pi}{4}\right) - That's better.
    Last edited by TKHunny; April 13th 2010 at 11:15 PM.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Sum and difference formula
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: April 11th 2010, 09:12 AM
  2. Difference Formula
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: March 17th 2010, 06:19 PM
  3. using the difference formula
    Posted in the Trigonometry Forum
    Replies: 6
    Last Post: November 6th 2009, 11:16 PM
  4. Central-Difference Formula
    Posted in the Calculus Forum
    Replies: 0
    Last Post: February 25th 2009, 04:42 PM
  5. Quick Question (Double Angle Formula)
    Posted in the Trigonometry Forum
    Replies: 4
    Last Post: December 11th 2007, 04:26 PM

Search Tags


/mathhelpforum @mathhelpforum