- #1

Bonus vir quid

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**SOLVED! :)**

## Homework Statement

The question is as follows;

Prove that (tan(A+B)-tanA)/1+tan(A+B)tanA = tanB

## Homework Equations

I'm certain the addition fomulae need to be applied, although I'm not entirely sure how. I genuinely have tried many times!

## The Attempt at a Solution

Okay, my first attempt was simply to work with the LHS, rewriting tan(A+B) as (tanA+tanB)/1-tanAtanB on both the top and bottom. I then tried to write tanA as sinA/cosA but this just made the LHS really messy and I wasn't able to cancel anything down.

I then tried to multiply both sides by (1+tan(A+B)tanA), leaving me with (tan(A+B)-tanA) = tanB(1+tan(A+B)tanA). I then expanded the brackets, rewrote all the tans as sin/cos and then attempted to cancel, but this again proved useless as I just ended up with a really really really messy equation.

I've tried this question many times and I still haven't managed to prove it. I am sure this is something very small that I'm missing/forgetting as this is the first trig question that I'm genuinely struggling with. I would appreciate if someone could nudge me in the right direction. Thank you in advance :).

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