Turn on thread page Beta
    • Thread Starter
    Offline

    1
    ReputationRep:
    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.

    Can someone please help me?

    Thanks
    Offline

    12
    ReputationRep:
    (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.

    Can someone please help me?

    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 !!
    • Thread Starter
    Offline

    1
    ReputationRep:
    (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?
    • PS Helper
    Offline

    14
    PS Helper
    (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 C=A+B, then then try and write B in terms of A and C. Having written B in terms of A and C, expand \tan B and compare with what you have.
    • Thread Starter
    Offline

    1
    ReputationRep:
    (Original post by nuodai)
    It's not what he meant. It might help you to write C=A+B, then then try and write B in terms of A and C. Having written B in terms of A and C, expand \tan B 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 :mad:
    Offline

    0
    ReputationRep:
    i tried subing the identity and it worked
    open the attachment to see the working.
    Attached Images
     
    Offline

    16
    ReputationRep:
    You want to use

    B = (A + B) - A
    • Thread Starter
    Offline

    1
    ReputationRep:
    (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
    Offline

    12
    ReputationRep:
    (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 .....
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: September 26, 2011

University open days

  • University of Roehampton
    All departments Undergraduate
    Sat, 17 Nov '18
  • Edge Hill University
    Faculty of Health and Social Care Undergraduate
    Sat, 17 Nov '18
  • Bournemouth University
    Undergraduate Open Day Undergraduate
    Sat, 17 Nov '18
Poll
Black Friday: Yay or Nay?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

Equations

How to use LaTex

Writing equations the easy way

Equations

Best calculators for A level Maths

Tips on which model to get

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.