Hi all,

I'm stuck with just one step now of a long problem.

Basically, how do I get from

to

I've been told I need to use just one trigonometric identity, but I honestly can't think of any that will do it?

Many thanks.

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- Aug 31st 2011, 11:22 AMSrengamWhich Trigonemetric Identity do I need to use?
Hi all,

I'm stuck with just one step now of a long problem.

Basically, how do I get from

to

I've been told I need to use just one trigonometric identity, but I honestly can't think of any that will do it?

Many thanks. - Aug 31st 2011, 11:28 AMSironRe: Which Trigonemetric Identity do I need to use?
Expand:

Afterwards use the fact - Aug 31st 2011, 11:40 AMSrengamRe: Which Trigonemetric Identity do I need to use?
Thanks but now theirs just one part I can't get after expanding,

how to get from

to

this is the only missing step now,

many thanks again. - Aug 31st 2011, 11:45 AMSironRe: Which Trigonemetric Identity do I need to use?
If you expand:

then you get:

Use so you get:

- Aug 31st 2011, 11:48 AMSrengamRe: Which Trigonemetric Identity do I need to use?
Thank you so much,

I really appreciate it. - Aug 31st 2011, 11:55 AMPlatoRe: Which Trigonemetric Identity do I need to use?
- Aug 31st 2011, 12:07 PMSironRe: Which Trigonemetric Identity do I need to use?