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Thread: This is Pissing me off

  1. #1

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    This is Pissing me off

    Can anyone remember the proofs of these Identities?


    Sin(a+b) = Cos(a)Sin(b) + Sin(a)Cos(b)
    Cos(a+b) = Cos(a)Cos(b) - Sin(a)Sin(b)
    If it wasn't for this sentence I wouldn't have a signature at all.

  2. #2
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    First, I thought of answering this, but then, I saw this page
    http://mathforum.org/dr.math/problems/susan5.16.98.html

    and they have done a good job..so I am off.
    Marriage - is not a word, but a sentence.

  3. #3
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    ...

    This question reminds me of how old i am....

    sin(A + B)

    sin A = cos(pi/2 - A)

    sin (A + B) = cos(pi/2 - (A + B))

    sin(A + B) = cos ((pi/2 - A) - B)

    sin(A + B) = cos(pi/2 - A)cosB + sin(pi/2 - A)sinB

    sin(A + B) = sinAcosB + cosAsinB

    http://users.erols.com/bram/identities.html

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