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# C4 double angle ids Watch

1. Hi everyone,

Suppose I've to integrate using double angle identities, I'm guessing the id I need is ?

My problem is I'm not sure how to get what I need to integrate in the form of the identity. If I let A=x for the numerator, the denominator is way off.
2. Let's look at this

Dividing top and bottom by and multiplying by will give you to integrate, this can be done easily with use of
3. (Original post by Robbie242)
Let's look at this

Dividing top and bottom by and multiplying by will give you to integrate, this can be done easily with use of

Thanks very much for your help. It's a little complicated for me!

If I follow your steps so I can understand it, I don't arrive at the same answer (I know you said I can just multiply but I wanted to it step by step to help me understand).

Dividing top and bottom by 2tanx:

Multiplying top and bottom by

A real mess! What did I do wrong?
4. (Original post by marcsaccount)
Thanks very much for your help. It's a little complicated for me!

If I follow your steps so I can understand it, I don't arrive at the same answer (I know you said I can just multiply but I wanted to it step by step to help me understand).

Dividing top and bottom by 2tanx:

Multiplying top and bottom by

A real mess! What did I do wrong?
You seem to have flipped things a bit

What I'd do is express your integral using the addition formulae before we divide

Now dividing top and bottom by will give the expression

5. ...but I don't understand the step you've taken here

(Original post by Robbie242)

How have you gotten from the denominator in the first fraction () to the denominator in the second fraction ()?

p.s sorry for being frustrating, and thanks for your time.
6. (Original post by marcsaccount)
...but I don't understand the step you've taken here

How have you gotten from the denominator in the first fraction () to the denominator in the second fraction ()?

p.s sorry for being frustrating, and thanks for your time.
It's fine don't worry.

Well you know our identity

we let and that gives us

To get that on the denominator, instead of writing we write on the denominator, hence the result above
7. (Original post by Robbie242)
It's fine don't worry.

Well you know our identity

we let and that gives us

To get that on the denominator, instead of writing we write on the denominator, hence the result above

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