Pre-Cal (Trig) Help?

The following relationship is known to be true for two angles A and B:

cos(A)cos(B)-sin(A)sin(B)=0.957269

Express A in terms of the angle B. Work in degrees and report numeric values accurate to 2 decimal places.

So I'm pretty lost on how to even begin this problem. I do know the product-to-sum identities such as cos(a)cos(b)=1/2(cos(a+b)+cos(a-b))
Any help is greatly appreciated!

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asked by Giovanni
  1. all you need is the sum formula for cosines.

    in other words,
    cos(A+B) = .957269
    A+B = 16.81°

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    posted by Steve
  2. Correction:
    Sum and difference identities is what I meant to say:

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

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    posted by Giovanni
  3. I tried putting in inverse cos(.957269) and the math site didn't like my answer. It tells me to enter it as an expression. Any ideas what I'm doing wrong?

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    posted by Giovanni
  4. try arccos(.957269)

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    posted by Steve
  5. It's still not working, weird.

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    posted by Giovanni

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