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!

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

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

    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)

    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?

    posted by Giovanni
  4. try arccos(.957269)

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

    posted by Giovanni

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