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!

Sum and Difference Formulas PROVE

  1. Nov 9, 2009 #1
    1. The problem statement, all variables and given/known data

    Given this formula

    Sum
    sin(a+b)=sin(a)*cos(b)+cos(a)*sin(b)

    prove this one
    Difference
    sin(a-b)=sin(a)*cos(b)-cos(a)*sin(b)

    Given this formula

    Sum
    cos(a+b)=cos(a)*cos(b)-sin(a)*sin(b)

    prove this one
    Difference
    cos(a-b)=cos(a)*cos(b)+sin(a)*sin(b)



    2. Relevant equations
    (difference and sum equations stated in the problem)



    3. The attempt at a solution
    I assume it's the same concept for both of them, i just don't know how to go about proving it to be true.
     
  2. jcsd
  3. Nov 9, 2009 #2

    Mark44

    Staff: Mentor

    a - b = a + (-b), so sin(a - b) = ?
     
  4. Nov 10, 2009 #3
    Like Mark44 said, use the fact that A - B = A + (-B).
    Hint: Sine is an odd function, which means that f(-x) = -f(x)
    2nd hint: Cosine is an even function, which means that f(-x) = f(x)

    That should do the trick.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Sum and Difference Formulas PROVE
  1. Proving Binomial Sums (Replies: 17)

Loading...