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February 17th, 2011, 05:32 PM  #1 
Newbie Joined: Feb 2011 Posts: 15 Thanks: 0  Trig Identities
I am studying for my DSP midterm, and I am stuck on some trig identities. I have this sample question: If the difference equation is y(n)=x(n) + x(n, and x(n)=cos(wn)*u(n), and w is equal to 2pi, and u(n) is the unit step, and n=8, express the answer in the form y(n)=A(cos(wn + B)). I have... y(=cos(w +cos(8w)^2 + sin(8w)^2 y(=cos(8w)+1 .... How can I simplify that further? 
February 19th, 2011, 02:25 PM  #2  
Math Team Joined: Apr 2010 Posts: 2,780 Thanks: 361  Re: Trig Identities
Hello Natalie, Quote:
The range of cos(8w)+1 is [0,2] A=0 would imply A=0, but A=2 implies well, A=2. Contradiction, therefore, You cannot write y(=cos(8w)+1 of the form y(n)=A(cos(wn + B)):=A(cos(w8 + B)).  
February 28th, 2011, 09:00 AM  #3 
Newbie Joined: Feb 2011 Posts: 15 Thanks: 0  Re: Trig Identities
Alright that makes sense as to why I cannot do that, but I still don't understand how to get it to that form.


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