x=sin(θ+7π12)+sin(θ−π12)+sin(θ+3π12)
2sin(2θ+π22)cos(2π32)+sin(θ+3π12)
=2sin(θ+π4)cos(π3)+sin(θ+π4)
=2sin(θ+π4).12+sin(θ+π4)
=2sin(θ+π4)
y=cos(θ+7π12)+cos(θ−π12)+cos(θ+3π12)
=2cos(2θ+π/22)cos(2π/33)+cos(θ+π4)
=2cos(θ+π/4).12+cos(θ+π/4)
=2cos(θ+π/4)
Now xy−yx=2sin(θ+π/4)2cos(θ+π/4)−2cos(θ+π/4)2sin(θ+π/4)
=sin2(θ+π/4)−cos2(θ+π/4)sin(θ+π/4)cos(θ+π/4)
=−2cos(θ+π/2)2sin(θ+π/4)cos(θ+π/4)
=2sin2θsin(2θ+π/2)=2sin2θcos2θ
=2tan2θ