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1. I have to prove that:

(tan(A+B) - tanA) / (1+tan(A+B)tanA) is equal to tanB

I've tried subbing in tan(A+B) is equal to (tanA+tanB) / (1-tanAtanB) but I just end up with huge fractions that don't seem like there gonna cancel down.

Thanks
2. (Original post by tinto99)
I have to prove that:

(tan(A+B) - tanA) / (1+tan(A+B)tanA) is equal to tanB

I've tried subbing in tan(A+B) is equal to (tanA+tanB) / (1-tanAtanB) but I just end up with huge fractions that don't seem like there gonna cancel down.

Thanks
It is much, much easier than what you have tried.

think how you can directly re-write (tan(A+B) - tanA) / (1+tan(A+B)tanA) using an identity not too dis-similar from the tan(A+B) that you tried !!!!

the answer falls out in perhaps 2 lines at most !!
3. (Original post by H.C. Chinaski)
It is much, much easier than what you have tried.

think how you can directly re-write (tan(A+B) - tanA) / (1+tan(A+B)tanA) using an identity not too dis-similar from the tan(A+B) that you tried !!!!

the answer falls out in perhaps 2 lines at most !!
I don't know of any other tan identities, aside from sin/cos. Is that what you meant?
4. (Original post by tinto99)
I don't know of any other tan identities, aside from sin/cos. Is that what you meant?
It's not what he meant. It might help you to write , then then try and write in terms of and . Having written in terms of and , expand and compare with what you have.
5. (Original post by nuodai)
It's not what he meant. It might help you to write , then then try and write in terms of and . Having written in terms of and , expand and compare with what you have.
i'm trying that at the moment with no luck

so if tan(A+B)=tanC, do I rewrite the whole thing as:

(tanC-tanA) / (1+tanCtanA)

even so, i still wouldn't know what to do from there. this is my homework after my second lesson of C3 trig, i managed to do all the others, this is the last one and i just can't do it
6. i tried subing the identity and it worked
open the attachment to see the working.
Attached Images

7. You want to use

B = (A + B) - A
8. (Original post by GANDULF)
i tried subing the identity and it worked
open the attachment to see the working.
thank you, im also gonna try using the A B and C terms to see if I can do it that way as well
9. (Original post by tinto99)
thank you, im also gonna try using the A B and C terms to see if I can do it that way as well
Write down the identity for Tan (x-y)

Now let x = A+B and let y=A substitute this in to the identity for Tan(x-y)

Now have a look at the thing and see why it helps with your problem .....

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