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# C3 integration help watch

Attachment 698706

My workings: https://imgur.com/a/cJALb
2. (Original post by Mystelle)

Attachment 698696
3. (Original post by RDKGames)
Sorry about that. Should be on now.
4. Are you sure this is C3? There isn't any integration in my C3 course that I've found.
5. (Original post by Mystelle)
Sorry about that. Should be on now.
You didn't integrate correctly.
6. (Original post by Mystelle)
Sorry about that. Should be on now.
U have to use trigonometric identities to rewrite (cosx)^4. I would suggest using the double angle formula for cos(2x) however it isnt a one step process.

Maybe rdk has a nicer method to use.
7. (Original post by Mystelle)
Sorry about that. Should be on now.
Use the reduction formula

8. (Original post by Mystelle)

Attachment 698706

My workings: https://imgur.com/a/cJALb
Which exam board are u? Perhaps we can tell u if u need to know this for c3 for ur exam board
9. cos4x

cos2xcos2x

{0.5{cos2x + 1}}2

0.25{cos22x + 2cos2x + 1}

can you continue ?
10. (Original post by Shaanv)
U have to use trigonometric identities to rewrite (cosx)^4. I would suggest using the double angle formula for cos(2x) however it isnt a one step process.

Maybe rdk has a nicer method to use.
There's a general reduction formula you can use but you still have to use it twice. There are also two identities you can use involving complex numbers, although the use of the identities doesn't actually require any knowledge of complex numbers.

If you raise both sides of the first identity to the power of four and expand using the binomial theorem, and then pair up the terms using the second formula you can easily solve for

It's a long method and I wouldn't recommend it, but it's one you can use. Here's an example using OP's question

Attachment 698718
11. (Original post by the bear)
cos4x

cos2xcos2x

{0.5{cos2x + 1}}2

0.25{cos22x + 2cos2x + 1}

can you continue ?
Thank you ever so much

Attachment 698724

PRSOM
12. (Original post by Mystelle)
Thank you ever so much

Attachment 698724

PRSOM

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