Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    0
    ReputationRep:
    Anybody know a way to remember double angle formulae after substitution? I know how to work them out but if i can remember that you make it a lot easier. Something for atleast the 2 equations I have *ed.
    sin 2x = 2sin x cos x
    cos 2x = cos2x -sin2x
    cos 2x = 2cos2x -1 *
    cos 2x = 1 - 2cos2x *
    tan 2x = 2tan x/ 1-tan2x
    Offline

    22
    ReputationRep:
    (Original post by Pink kitten)
    Anybody know a way to remember double angle formulae after substitution? I know how to work them out but if i can remember that you make it a lot easier. Something for atleast the 2 equations I have *ed.
    sin 2x = 2sin x cos x
    cos 2x = cos2x -sin2x
    cos 2x = 2cos2x -1 *
    cos 2x = 1 - 2cos2x *
    tan 2x = 2tan x/ 1-tan2x
    Practice using them and they become second nature.
    • Very Important Poster
    Offline

    21
    ReputationRep:
    Very Important Poster
    (Original post by Pink kitten)
    Anybody know a way to remember double angle formulae after substitution? I know how to work them out but if i can remember that you make it a lot easier. Something for atleast the 2 equations I have *ed.
    sin 2x = 2sin x cos x
    cos 2x = cos2x -sin2x
    cos 2x = 2cos2x -1 *
    cos 2x = 1 - 2cos2x *
    tan 2x = 2tan x/ 1-tan2x
    As above, practice, practice, practice!
    and the secret ingredient...
    Spoiler:
    Show
    practice!


    then you will have no trouble remembering them

    There are plenty of exercises in textbooks to work from.
    Offline

    3
    ReputationRep:
    (Original post by Pink kitten)
    Anybody know a way to remember double angle formulae after substitution? I know how to work them out but if i can remember that you make it a lot easier. Something for atleast the 2 equations I have *ed.
    sin 2x = 2sin x cos x
    cos 2x = cos2x -sin2x
    cos 2x = 2cos2x -1 *
    cos 2x = 1 - 2cos2x *
    tan 2x = 2tan x/ 1-tan2x
    For the two you have *ed it takes a matter of seconds to arrive at them from the one above ( using sin^2x + cos^2x = 1), so it is not necessary to remember them. As for the rest, as the others said, do loads of questions involving them!

    Alternatively deriving them a few times can help.
    Offline

    10
    ReputationRep:
    (Original post by Pink kitten)
    Anybody know a way to remember double angle formulae after substitution? I know how to work them out but if i can remember that you make it a lot easier. Something for atleast the 2 equations I have *ed.
    sin 2x = 2sin x cos x
    cos 2x = cos2x -sin2x
    cos 2x = 2cos2x -1 *
    cos 2x = 1 - 2cos2x *
    tan 2x = 2tan x/ 1-tan2x
    You can derive them in like 10s off the formula sheet anyway since you have sin(a+b) cos (a+b) on there, but when you do a lot of past papers they become pretty much second nature anyway
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Have you ever participated in a Secret Santa?
    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

    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
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • 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

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