Expand cos(16b) using a double angle identity in terms of sines.

Firstly, next time could you repeat your question in the body of your post please.

 

\(cos(16b) \\= cos(8b+8b)\\=cos^2(8b)-sin^2(8b)\\=(1-sin^2(8b))-sin^2(8b)\\ =1-2sin^2(8b)\)

 

 

that probably answers the question :)