Tough Twelve Trig Formulas

1. Dec 15, 2007

Quinn Morris

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

2. Dec 15, 2007

dynamicsolo

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?

3. Dec 16, 2007

Quinn Morris

so times buy a form of one...... 1 over cosacosb?

4. Dec 16, 2007

rock.freak667

yes that is correct, divide the numerator and denominator by cosacosb