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Homework Help: Adding cosine functions

  1. Jan 23, 2010 #1
    1. The problem statement, all variables and given/known data

    Hi guys,

    I don't know if this should go here because it is an excerpt from a higher level problem. The part where I get stuck is when I try to add the cosine functions.

    Is there any way to add sine and cosine functions that have a scalar in front that cannot be factored out? For example:

    5*cos(wt) + 6*cos(wt + pi/4)

    If there weren't any numbers in front of the functions then I could use the trig identity. What can I do with the numbers there? Thanks
  2. jcsd
  3. Jan 23, 2010 #2


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    Homework Helper

    5cos(wt) + 6*cos(wt + π/4)

    expand out cos(wt+π/4) then group the like terms. Then you can either put in the form Rcos(wt±A) or Rsin(wt±A)
  4. Jan 24, 2010 #3


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    cos(A+ B)= cops(A)cos(B)- sin(A)sin(B).
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