Turn on thread page Beta
    • Thread Starter
    Offline

    2
    ReputationRep:
    How does sin^2(2x)= (1-cos(4x))/2 ? I just can't work it out!

    Thanks!
    Offline

    22
    ReputationRep:
    (Original post by rpnom)
    How does sin^2(2x)= (1-cos(4x))/2 ? I just can't work it out!

    Thanks!
    Re-arrange the double angle formulae for \cos 2A to get:

    \displaystyle \cos 2A = 1 - 2\sin^2 A \iff \sin^2 A = \frac{1- \cos 2A}{2}, agree?

    Then set A = 2x.

    Also, moved to maths.
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by Zacken)
    Re-arrange the double angle formulae for \cos 2A to get:

    \displaystyle \cos 2A = 1 - 2\sin^2 A \iff \sin^2 A = \frac{1- \cos 2A}{2}, agree?

    Then set A = 2x.

    Also, moved to maths.
    Thank you so much! It seems so simple now! I was trying to figure it out for ages!
    Offline

    22
    ReputationRep:
    (Original post by rpnom)
    Thank you so much! It seems so simple now! I was trying to figure it out for ages!
    No problem, it comes in useful all the time when integrating squared trigonometric functions. Remember that also:

    \displaystyle 

\begin{equation*}\cos 2A = 2 \cos^2 A - 1 \iff \cos^2 A = \frac{\cos 2A + 1}{2}\end{equation*}
    Offline

    19
    ReputationRep:
    I am 1 hour too late
 
 
 
The home of Results and Clearing

2,776

people online now

1,567,000

students helped last year

University open days

  1. SAE Institute
    Animation, Audio, Film, Games, Music, Business, Web Further education
    Thu, 16 Aug '18
  2. Bournemouth University
    Clearing Open Day Undergraduate
    Fri, 17 Aug '18
  3. University of Bolton
    Undergraduate Open Day Undergraduate
    Fri, 17 Aug '18
Poll
Do you want your parents to be with you when you collect your A-level results?
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

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.