Results are out! Find what you need...fast. Get quick advice or join the chat
x

Unlock these great extras with your FREE membership

  • One-on-one advice about results day and Clearing
  • Free access to our personal statement wizard
  • Customise TSR to suit how you want to use it

1 - cos2x

Announcements Posted on
Had your SQA results? Find your uni forum to get talking to other applicants, existing students and your future course-mates 04-08-2015
Competition: win a karting session for you and seven mates! 24-07-2015
  1. Offline

    ReputationRep:
    is

    1 - cos2x equal to (sinx)^2

    ??????thanks:confused:
  2. Offline

    Nearly. It's equal to 2(sinx)^2. Proof is from the double angle formula.
  3. Offline

    ReputationRep:
    No

    Rule is

    cos^2 x + sin^2 x =1
  4. Offline

    ReputationRep:
    (Original post by tommm)
    Nearly. It's equal to 2(sinx)^2. Proof is from the double angle formula.
    thanks.

    is that just one of the ones we have to remember?
  5. Offline

    (Original post by rye225)
    No

    Rule is

    cos^2 x + sin^2 x =1
    You're thinking of the wrong rule; the rule you want is the double angle formula for cosine.

    (Original post by sonic23)
    thanks.

    is that just one of the ones we have to remember?
    You're given \cos (A+B) = \cos A \cos B - \sin A \sin B, so you can derive \cos 2x = \cos^2 x - \sin^2 x and play with it until you get it in the right form... but it's worth remembering these three, if nothing else:
    \newline \cos 2x = \cos^2 x - \sin^2 x\newline

= 2\cos^2 x - 1\newline

= 1 - 2\sin^2 x

    Then you can rearrange it.
  6. Offline

    (Original post by sonic23)
    thanks.

    is that just one of the ones we have to remember?
    Pretty much, yes. As an experienced A-leveller, I can immediately recall \cos 2x = 2 \cos^2 x - 1 = \cos^2 x - \sin^2 x = 1 - 2 \sin^2 x, but that's because I've used it so many times. Practice makes perfect.
  7. Offline

    ReputationRep:
    (Original post by nuodai)
    You're thinking of the wrong rule; the rule you want is the double angle formula for cosine.


    You're given \cos (A+B) = \cos A \cos B - \sin A \sin B, so you can derive \cos 2x = \cos^2 x - \sin^2 x and play with it until you get it in the right form... but it's worth remembering these three, if nothing else:
    \newline \cos 2x = \cos^2 x - \sin^2 x\newline

= 2\cos^2 x - 1\newline

= 1 - 2\sin^2 x

    Then you can rearrange it.

    thanks
  8. Offline

    Not a problem.

Reply

Submit reply

Register

Thanks for posting! You just need to create an account in order to submit the post
  1. this can't be left blank
    that username has been taken, please choose another Forgotten your password?
  2. this can't be left blank
    this email is already registered. Forgotten your password?
  3. this can't be left blank

    6 characters or longer with both numbers and letters is safer

  4. this can't be left empty
    your full birthday is required
  1. By joining you agree to our Ts and Cs, privacy policy and site rules

  2. Slide to join now Processing…

Updated: March 3, 2009
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

Poll
Uni students: did you know what you wanted to do when you left school/college?
Results and Clearing

SQA results chat

Come talk about your results here

new on tsr

Indian? Join the society here

Take part in the chat and make friends

Study resources
x

Think you'll be in clearing or adjustment?

Hear direct from unis that want to talk to you

Get email alerts for university course places that match your subjects and grades. Just let us know what you're studying.

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