log16 (1+cosπ/8)(1-cosπ/8)+2log16 cosπ/8= log16 (1-cos²π/8)+lod16 cos²π/8=
log16 (sin²π/8)+log16 cos²π/8= log(4²) (sin²π/8*cos²π/8=1/2log4 sin²π/8cos²π/8=
=log4 (sin²π/8cos²π/8)^1/2= log4(sinπ/8cosπ/8)=log4 (2sinπ/8cosπ/8)/2)=
=log4 (1/2sin π/4)=log4 1/2= 1/2*-1log2 2=-1/2