-cos(π/16)sin(π/16)cos(π/8)
=(-1/2)·2cos(π/16)sin(π/16)cos(π/8)
=(-1/2)·sin(π/8)cos(π/8)
=(-1/4)·2sin(π/8)cos(π/8)
=(-1/4)·sin(π/4)
=(-1/4)·(√2/2)
=-√2/8.
-cos(π/16)sin(π/16)cos(π/8)
=(-1/2)·2cos(π/16)sin(π/16)cos(π/8)
=(-1/2)·sin(π/8)cos(π/8)
=(-1/4)·2sin(π/8)cos(π/8)
=(-1/4)·sin(π/4)
=(-1/4)·(√2/2)
=-√2/8.