=2(cos(x)*cos(x)-1/2)^2/(2tan(π/4-x)cos(π/4-x)^2)
=(1/2)*cos^2(2x)/[2sin(π/4-x)*cos(π/4-x)]
=(1/2)*cos^2(2x)/sin(π/2-2x)
=(1/2)cos(2x)