How do you express $cos (\frac{15 π}{8}) \cdot cos (\frac{13 π}{12})$ $cos( (15 pi)/ 8 ) * cos (( 13 pi) /12 )$ without using products of trigonometric functions?

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Answer 1 · 2016-07-16T09:38:44

$\frac{1}{2} [cos (\frac{19 π}{24}) + cos (\frac{23 π}{24})]$ $1/2 [ cos ( (19pi)/24) + cos ((23pi)/24)]$

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How do you express cos( (15 pi)/ 8 ) * cos (( 13 pi) /12 ) cos(15π8)⋅cos(13π12)cos( (15 pi)/ 8 ) * cos (( 13 pi) /12 ) without using products of trigonometric functions?