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avatar+578 

its been a while...but im back. i've been working really hard and finally have another question.

 

is \(cos(\theta + \frac{\pi}{2} = -sin(\theta)\) a true identity?

 May 29, 2018
 #1
avatar+19934 
+1

Here is a graph of  cos (x + pi/2):

 

 

 

 

and here is a graph of  - sin x :

 

 

 

 

 

 

 

WHat do you think?

 May 29, 2018
 #2
avatar+106536 
+1

We can use the angle sum identitiy for the cosine to  check this  ........

 

cos  (θ  + π/2) = 

 

cos θ cos π/2  -  sin  θ sin π/2  =

 

cos θ *  ( 0 )  - sin θ  * (1)  =

 

-sin θ

 

So...this is an  identity  !!!

 

 

 

cool cool cool

 May 29, 2018
edited by CPhill  May 29, 2018

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