1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    User Avatar
    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


    User Avatar
    Science Advisor

    cos(A+ B)= cops(A)cos(B)- sin(A)sin(B).
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook