Math Is Fun Forum

Peaches47

Member

Registered: 2008-02-17

Posts: 13

Why are Completing Identies SO HARD!!!!!!

Help... My book has got to be crazy.. I just don't get the concept.  All through the text book says "verify" and my chapter test says "complete".  The end of chapter included radians which really confuse me.  Here they are.

sin(x+3pi/2) =?

what about

tan(pi - θ)= ?      (wouldnt that just be -tan θ ?)

sin² θ/2=?

I am just lost with this stuff... can someone provide some detail explainations.  Learning from the text in the book atleast provided the "=" so that I could figure it out.

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Struggling Middle Aged Math Student

JaneFairfax

Member

Registered: 2007-02-23

Posts: 6,868

Re: Why are Completing Identies SO HARD!!!!!!

For tan, use the identity

.

And for the last one, rearrange the identity

.

Peaches47

Member

Registered: 2008-02-17

Posts: 13

Re: Why are Completing Identies SO HARD!!!!!!

Thank you Jane that was very helpful,  however you lost me on that last one.

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Struggling Middle Aged Math Student

JaneFairfax

Member

Registered: 2007-02-23

Posts: 6,868

Re: Why are Completing Identies SO HARD!!!!!!

Maybe you recognize this identity better:

Well then, replace A by

and you have it.

Peaches47

Member

Registered: 2008-02-17

Posts: 13

Re: Why are Completing Identies SO HARD!!!!!!

oh  Thank You Jane... I see it now....

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Struggling Middle Aged Math Student