How do I prove this identity. The only thing I know is that I have to use a product to sum formula, but which one?
i thought only clues or a little help (not complete solution) will be given on the first day?
we will use this: , yes cos(A - B), you will see the pattern once you apply it.
Numerator = N = cos 66 cos 6 + cos 84 cos 24 = cos 66 cos 6 + sin 6 sin 66
Denominator = D = cos 65 cos 5 + sin 5 sin 65
N/D = ?