February 23rd, 2013, 01:05 AM  #1 
Newbie Joined: Feb 2013 Posts: 3 Thanks: 0  So confused with this
Heres the Q: Two signals are received at a satellite tracking station. They are modelled mathematically by the functions: f(t) = 10cos(16t + pi) g(t) = 10cos (20t  pi) The signals are added together, i.e. the function h(t) = f(t) + g(t) is formed. (a) Use trigonometric formulae to obtain the function h(t). (b) Obtain a graph of the function h(t). (c) Find an expression for dh/dt using the product rule and showing all workings out Now i know what a cosine wave looks like, but i really have no idea how to do this?? 
February 23rd, 2013, 01:18 AM  #2 
Senior Member Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,211 Thanks: 521 Math Focus: Calculus/ODEs  Re: So confused with this
Since you are instructed to differentiate using the product rule, you need to use the sumtoproduct identity: Then you could use: Can you proceed? 
February 23rd, 2013, 02:36 AM  #3 
Newbie Joined: Feb 2013 Posts: 3 Thanks: 0  Re: So confused with this
Ive never seen that equation. Oh dear

February 23rd, 2013, 02:41 AM  #4 
Senior Member Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,211 Thanks: 521 Math Focus: Calculus/ODEs  Re: So confused with this
Can you apply it?

February 23rd, 2013, 02:58 AM  #5 
Newbie Joined: Feb 2013 Posts: 3 Thanks: 0  Re: So confused with this
Ive tried to have a go, but im really confusing myself

February 23rd, 2013, 10:01 AM  #6 
Senior Member Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,211 Thanks: 521 Math Focus: Calculus/ODEs  Re: So confused with this
I would begin with: Now, applying the sumtoproduct identity, we have: Now using the identities and we have: 

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