cos^2(3π/8) - sin^2(3π/8)
cos^2(x) - sin^2(x) = cos(2x)
cos^2(3π/8) - sin^2(3π/8)=
cos(2*3π/8)=
cos(3π/4)=
cos(π/4 +π/2)
cos(x+y)= cos(x)cos(y) - sin(x)sin(y)
cos(π/4 +π/2)=
cos(π/4)cos(π/2) - sin(π/4)sin(π/2)
cos(π/4) = 1/√2
sin(π/4) = 1/√2
cos(π/2) = 0
sin(π/2) = 1
cos(π/4)cos(π/2) - sin(π/4)sin(π/2)= -1/√2
