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How does my book go from this step to the next (trig)

  1. Apr 10, 2008 #1
    OK, in an example, we are given:

    "T(θ)= 2 cos^2 (θ) +sin^2 (θ) − sin (θ) + 3
    =cos^2 (θ) − sin θ + 4.
    Then Tθ(θ)= −2 cos θ sin θ − cos θ =
    −cos θ(2 sinθ + 1)"

    can anyone explain what happened from step 1 to 2--i am completely lost?

  2. jcsd
  3. Apr 10, 2008 #2


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    [tex]\sin^2 \theta + \cos^2 \theta = 1 [/tex]
    [tex]\sin^2 \theta = 1 - \cos^2 \theta[/tex]
    Now, substitute in for step 1 and simplify.
  4. Apr 10, 2008 #3
    Geez, I am embarassed.
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