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Homework Help: Proving Trig Identities

  1. Mar 23, 2010 #1
    1. The problem statement, all variables and given/known data
    Prove Trig. Identities

    1. sec θ (sec θ - cos θ)= tan^2 θ

    2. Relevant equations

    sec θ = 1/cos θ
    tan θ = sin θ/ cos θ
    cot θ = cos θ / sin θ

    3. The attempt at a solution

    1. sec θ * sec θ - sec θ * cos θ

    1/ cos θ * 1/ cos θ - 1/ cos θ * cos θ

    ----> cos θ is crosses out by the right but im confused on 1/cos θ. I know 1/cos θ = sec θ. Wait does this problem refer to the pythagorean identity which is 1 + tan^2 θ = sec^2 θ
     
  2. jcsd
  3. Mar 23, 2010 #2

    Mark44

    Staff: Mentor

    Use = !
    Generally you want to start on one side and end up with the expression on the other side.

    sec θ * sec θ - sec θ * cos θ = sec2θ - 1 = ?

    In answer to your question, yes.
     
  4. Mar 23, 2010 #3
    Thanks a lot :)
     
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