1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Tough Twelve Trig Formulas

  1. Dec 15, 2007 #1
    1. The problem statement, all variables and given/known data

    Prove that: tan (a - b) = tana - tanb
    1 + tanatanb

    2. Relevant equations

    cos (a- b) = cosacosb + sinasinb

    sin (a - b) = sinacosb - cosasinb

    3. The attempt at a solution

    I have plugged in the two equations give above since tan - sin/cos and then i'm am stumped of how to proceed

    tan (a - b) = sinacosb - cosasinb
    cosacosb + sinasinb

    can anyone help please?
  2. jcsd
  3. Dec 15, 2007 #2


    User Avatar
    Homework Helper

    The formula you are trying to arrive at provides the clue: what could you divide numerator and denominator by to get that "1" in the denominator?
  4. Dec 16, 2007 #3
    so times buy a form of one...... 1 over cosacosb?
  5. Dec 16, 2007 #4


    User Avatar
    Homework Helper

    yes that is correct, divide the numerator and denominator by cosacosb
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook