2sin(x-4/π)sin(x+4/π)

2sin(x-4/π)sin(x+4/π)


=2sin(x-π/4)cos[π/2-(x+π/4)]
=2sin(x-π/4)cos(π/4-x)
=2sin(x-π/4)cos(x-π/4)
=2sin[2(x-π/4)]
=2sin(2x-π/2)
=-2cos2x